I purchased the Pterodactyl last Spring and love it.
The Pterodactyl is a little pricey, but it is definitely a high quality backplate. You can tell by looking at it that Critical Aspect takes pride in its product.
The two D-rings on the backplate are the lower attachment points for stage bottles even though they look like they stick out waiting to latch on to anything you swim by they don't, they are angled inward so that the front of the D-ring just rests against your waist.
It also has a deeper "V" which I guess provides a little more stability for doubles it also keeps the wing nuts a little father from your back.
The best feature about it I think is the harness rollers on the lower corners of the backplate which makes it far easier to adjust and cinch up the harness.
I havent had any problem with it riding up on me because it doesnt have a crotch strap but there is a 1" slot in the backplate for the addition of one if you like, of coarse on most backplates the crotch strap is usually an option. You definitely don't need a chest strap,mainly due to the harness rollers which enable you to cinch up the entire harness.
I also purchased the STA which also works extremely well, securing a single very solid to the backplate also it sets the tank about an 2" off of the backplate.
These is just my personal experience with the Pterodactyl, in my opinion it works as advertised.
