What about the decomp if they take the poison and go back into the walls?

We put the trays down and while possible that could happen, especially in hot weather, we haven't smelled any decomp and were willing to put up with a possible smell for a few days to rid ourselves of the problem

You will have a stinky funk that comes through the walls. It will go away in about 3 weeks if you can't remove the dead animal.

There is no poison with this product. You put bait (peanut butter works great) and when the mouse enters the trap the wall closes on them, usually killing them but even if it doesn't the're stuck in the trap.

Assuming thus question is about the spin trap. They cannot go in to get bait and come out. It closes shut and they are stuck.