A rack system is nice because you can keep numerous animals in a small amount of space. Some rack system are designed to have lids while others do not. Without having lids on the tubs you are able to pull the tubs out a little to feed or change water, with lids, you would have to slide the entire tub out in order to remove the lid. Another benefit I like about rack systems is that the snakes have a nice dark spot in the back that provides them with a sense of safety and security while at the same time provides light in the front so you can still have the day night cycle.
I've never had a single escape using a rack system, that doesn't mean escapes can't happen but i've never had one.
The tubs slide over the heat tape, most rack systems have the heat tape machined into the rack so the tubs do not actually touch the tape. I do not see a problem with the heat tape effecting the tubs below.

Which rack were you looking at?

Hope that helps you out.