I have used both of those exo terra products, mixed with some normal soil/leaf mould i collect from a local forest. They are both ok, but now i just use the soil/leaf litter i collect from the forest, as it's free & works better as a bio active substrate. Also comes with free clean up crew... But watch out for slugs/snails or their eggs.

As for when to change the substrate. In a word, Never! The whole idea is to get it set up so that the clean up crew, multiply & so recycle any waste, i.e poo or any mould/rotting veg & animal matter (dead crickets, roaches etc). Then as Mike said, no need to clean the tank, the bugs do it all for you.