I've seen them at shows, felt them, lifted them and have seen a GTP in one.
They are HDPE much like Visions, but they have no ridges on the floor (that is a good thing) and no door lip for snakes to hide on top of (also a good thing.) The colors are nice too. Another good thing. And they have a heat shroud and a heat pad recess and a cord exit path. More good things.
I don't see why they wouldn't work just nicely.
Depends on the colubrids of course. Although the cages will work for any colubrid, I wouldn't pay the money for any plastic cage if you are housing something small like Mexican milks or hognose, etc where a sweaterbox or inexpensive glass tank is plenty roomy and far less expensive. I would even question expensive plastic cages for kings/milks that spend 99.9% of their time in or under the surface of the substrate, even though the cages will work fine in those cases too. A cornsnake on the other hand would look great because you could have some branches, and the snake would use them to bask sometimes.