I have the £29.99 one which I bought from Lakeland a few years ago. It makes lovely yoghurt and is easy to do. You just boil the milk in a pan, wait until it cools, put it in the maker and leave it.
It makes big portions, so one 'making' will probably last two several days.
Genuinely think it's nicer than most yoghurt you can buy. The main reason I bought it was I wanted to cut down on my single use plastic and not buy all those yoghurt pots.
It has never gone wrong, even on the occasions when I've taken my eye off the ball and thought I'd messed it up. I always use semi-skimmed milk but you can use any milk and all you do is adjust the time. The guidebook is very easy to follow.
You need to have or buy a thermometer as the temperature of the milk is the vital bit.