1) I have several from three different manufacturers. I purchased them all used on local classified forums for reptiles or Craigslist. Yes they are worth the money, even if I had to pay full retail for them.

2) They are ok, not as good as melamine but I keep my snakes in a room that has supplemental heat so the rest of the house can be cold in the winter while that room is warm.

3) Downsides to melamine: it is heavy and since the interior is wood it does swell a bit in high-humidity environments. Downside to PVC is its costly compared to melamine.