(No connection etc)
Just got a set of these:
and I am very impressed. Certainly gives me a huge confidence boost and does indeed level up things on sloping ground. For the size and the cost, I'd thoroughly recommend them to anyone who does ladderwork (unless your ladder is already fitted with adjustable grippy feet of course!).
Using in conjunction with an old cheap ali ladder (still sound) and a stand off:
which is surprisingly (very) solid considering it comes as a box of bits.