The disadvantage with foam is that it can VERY easily get mouldy. If you do decide to use foam to make hides, check it regularly for mould.
The other issue, obviously, is cleaning them/getting rid of bacteria is pretty much impossible. Be prepared to replace them a few times a year at least.
I'm pretty sure I know which foam hides you're talking about... We discontinued them at work, and I have a feeling it's probably due to the two reasons above. They're nice in theory, but in a moist, humid environment, foam turns into a mould farm.