I bought a pair of those for use with a pair of Skechers I have with really hard and rather unsupportive insolves. They work pretty well, I guess. They make my feet move around in the shoe a little more than normal, but it's no problem. They really do improve the shoes, though.
The only problem is that they'll shift and bunch up if you dance too hard on them, which is very uncomfortable.
Also, I'm just glad I didn't have to trim them down, as that seems like a pain.