I don't have any experience with that product but I owned a tent trailer for two years which is a similar concept. It wasn't a great experience, I actually think they are colder due to the underaide being exposed and they mold very quickly if put away wet so there was a lot of setup/tear down involved. Those are probably obvious answers but just wanted to provide some perspective.

 

I had one also for a tent trailer years ago. Mine had a floor and attached across the bottom of the trailer body. Truly was a added room, best addition to our trailer setup. I bought the room for a Elk hunt in Colorado's rifle season, yes it snowed some, rained too. It held up fine. It was a 8x8, that extra 64 sf made a awesome difference with the weather we had storing extra gear dry and a spot to remove rain gear and boots instead of inside the trailer,,,gregg

 

I had one also for a tent trailer years ago...

Did you have yours custom-made? If so, where?

Was it canvas or more tent-like material?

 

Looks like a great idea

 

It would nearly double my current square-footage...

My concerns are (not necessarily in this order):
1) Cost
2) Durability
3) Performance in inclimate weather

 

And add a room to your awning for even more space.