Sani Chips are aspen, they are just chipped instead of shredded.
So yes, if you leave your enclosure wet for long periods of time, it will mold. I don't consider this to be a "con" for aspen as you should be spot cleaning messes and water bowl spills within a day or two of their occurrence. Aspen should not mold within a few days.
I use them...they are ok, but I wouldn't recommend them. They stick to everything. If you use them you absolutely MUST feed your snake in a different tank. They also don't let heat through at all so you probably have to remove the bedding from under the warm side hide and put a piece of paper under it to protect your snake from the glass.