Heng's escape hatch on roof

I had one of these on my old Datsun P/U camper. I was about 18" taller than the camper, and when I wanted to get dressed, stretch or just check things out, I'd open up the hatch. I am looking at getting a low profile (5' high interior) CT to convert and plan on installing one. I don't recall what brand my camper had in it, but is anybody familiar with this companies hatches?
http://www.hengsindustries.com/vents_other.html

http://www.hengsindustries.com/vents_other.html
