I have a cheap halfords one, bright red so you dont loose it.

It was being used virtually every weekend and I've even left it overnight holding a corner up (I know you're not meant to).
No problems yet.
On the Minor i'd jack the whole back end up from the diff casing easy enough.
The jack has never gone down or leaked.

The only problem is, the small ones dont have much lift height so you end up messing about with blocks of wood on occasion.