They're ok for what they are - ie cheap and small, easy to carry in the boot of your car. However, it's not going to stop you from crouching down and doing your back in is it (like us old folk have to worry about!) I'd pay a bit extra and get a full size workstand.
No way is swmbo going to agree to £??? on a workstand, I'll either have to keep 'em peeled for someone to offer a bargain or (finally) learn to weld and make one (old bike frame looks like it might do the job ok??)...