So we decided that this year's present for grandmas would be digital photo frames. I must be the only person who hadn't really seen one before! Apparently they were the must-have gift last christmas.

Anyway. What to buy? They range from £40 to £200. The predominant factor would appear to be screen size; the bigger the screen the more expensive. However when you look a bit closer you find that you can get a 7" screen for £50 or £150. What can be that different? Well, the top price ones offer higher resolution (more dots making up the picture) and even wireless connectivity so you can update the picture frame from your PC as if by magic.

Being a bit of a skinflint it seemed that a standard £50 unit would be just the job so despatched she-who-must-shop to Argos to buy a pair of Agfa machines. When they arrived back (with lots of other unordered items I might add) I decided we really ought to try them out and make sure they work.

The first thing you notice is that when you see them in the shop they generally have very close up and colourful pictures displayed on them. However my photos seem to contain a lot of landscapes and shots of people and surroundings rather than just people. So the having a 7" display way across the room is really rather disappointing. Would you look at a 6x4 photo from across the room? No of course not, you'd hold it in your hand. So it's not really an adornment for the mantelpiece but probably better something a bit closer to where you're sitting.

Next, everytime I turned the damned machine on it would start displaying the pictures from the beginning again. If I've got 2000 photos changing every minutes it's going to have to be on for 33.33 hours until I get to the last one. In reality I'll never see it.

And then there's the whole question of turning on and off. Am I really going to turn it on when I get up and off when I go to bed? No. Well, maybe for the first few days. Then I'll leave it off until the evening. Then it'll start getting left off until someone visits. Then sometime in the future visitors will start asking what "that dark photo" is and it'll get put in a cupboard. After all, when I turn it on I'm going to see that damned picture again! It's no real effort to turn on and off but you do have to keep making a decision "shall I turn it on?" and making decisions gets wearing.

And what else is annoying? The fact that the maximum you can set before the next photo is displayed is 1 minute. I  want it to change every 30 minutes. If it keeps changing it'll be annoying and intrusive.

So clearly this was no good. What's really annoying is that the usability problems (and let's not get on to confusing menus and buttons) can all be solved in software. And software is pretty cheap. Writing the bit of code that selects pictures at random is just not that hard. Allowing the user to select 1 hour or 1 minute is not rocket science.

And that's when I realised that the higher models had better software with better features. It costs virtually nothing to put better software in the cheap models but then there would be no product differentiation. It reminds me of when cars would have a list of extras you could choose - all of them really expensive. In some cases all car models would have the gizmos in place but when you paid the extra £100 they would put the 50p switch in that would enable you to use it (intermittent wash wipe springs to mind).

So, those went back to Argos and purchased a pair of £99 Samsung units. Annoyingly the Argos website gives you very little specification and doesn't give you model numbers so you can't look up the details elsewhere. But the Samsungs promised some sort of random/shuffle play and also had an auto-on/off timer.

Great!

No. It was rubbish.

All the photos have to be in the root directory of the memory stick. Which is ok as long as you don't have photos with the same filename. Which I do because I let the camera name the files automatically, names such as "DSC00001.JPG". And I do end up with photo files with the same name. So now I have to start renaming files to avoid conflicts rather than leaving them in folders.

I set the option to "shuffle display" and turned it on. Watched the first few pictures, yup, random order, so switched off and on again. And it started again showing the photos in random order. Unfortunately it was exactly the same random order as last time. And everytime I switched it off and on it did exactly the same.

I was really quite cross. There is no obvious resource on the internet where you can see comparisons of the different digital frames. Trying to research the individual units by looking their manuals up on the interweb is very time consuming and frustrating.

So back they go to Argos.

It is impossible to buy one of these machines and have a clue what you're getting. But it's near Christmas and it's time to get serious. So I load up my USB memory stick with photos and trodge off to the one of the most loathesome shops on the planet - PC World.

Every one I tried (under £120) was useless. I "educated" about half a dozen people whilst I was experimenting. The number of people who are buying these machines based on the idea concerns me about just how many will end up neglected in the corner in a few months because they are so poorly designed.

There is a clear difference in picture quality between the £50 and £100 machines. Unless you have lots of close up shots then don't bother with the cheap ones. Really, don't. Everything is blurry

There was one digital frame that wasn't working, a Toshiba Tekbright. £100 so within budget. Eventually I got one of the staff to get another one out of a box and I had a look at the manual. No random mentioned. Oh dear. But I decided I'd have a go. Unfortunately I couldn't plug the USB dongle in as for some reason Toshiba had decided that I wouldn't want to do that (unlike every other manufacturer) so I had to rely on the demo pictures already loaded.

I had a look through the menus expecting the worse but, hang on!, there was a "random" option (not documented in the manual). Tried it - it worked! Turned off and on. 1st picture was the same but from then on it showed random photos. Off and on again. Same deal! Hurrah. The menu system was the most intuitive yet and the picture quality very good. Oh, and it has an auto-on/off timer so you can set it to turn itself on and off all by itself everyday.

A quick call home and discovered the unit was £90 in John Lewis so after a quick chat with the salesman he agreed to do the same deal.

Then I went off to have a look for memory cards. They are desperately expensive in PC World. I guess it's a classic sales technique - sell the main product for a good price and people will assume the accessories are a similarly good price. Nope, I think this is where they make their money. A bit like with inkjet printers - virtually give the machine away and then charge through the nose for some coloured water. Needless to say I left without the memory cards.

Got the machines home and decided to give them a test drive. Loaded some photos up. It worked fine. I could set the maximum time to an hour and really was random! You can even select to have it display the time permanently in the corner. Which then gave me the idea of something else to test. What happens when you have a power cut? I turned the power off for 5 seconds and then back on. Of course it forgot the time. Why? WHY? W H Y? How hard to put a little backup battery in? Not at all. Would add about 10p to the build cost.

So, after all this grief I can save you the trouble. Hopefully you now know what to look for and what not to look for. And if you want to save time just go and buy a TOSHIBA TEKBRIGHT