I spent a lot of time looking for a stool for my son to stand on. I initially bought a wooden one, and anyone who has looked into this will know that that costs over £25.
At first I was hesitant to buy this item because it seemed so cheap versus the wooden stools, and because I thought it might slide around.
However, it is very durable. It has a rubber edging to the bottom of the stool and doesn't slide around even on our wooden floor and has little raised sections on the top to give the child's feet some grip.
The only downside is that my son is now 2 and that the middle of the stool does sag a little when he stands on it (although he is big for his age) - at some point it will break, but given the price I will not be too upset.
Originally I bought the Pintoy Wooden Step Stool (Amazon sell this, so take a look) and I am as happy with this plastic stool as with the wooden one, only this stool is 1/5 of the price (I now own 2)!