I have the GIK Tri-traps and the Mondo traps. I can't vouch for their individual effectiveness because they're in a room with both Real traps and some other GIK bass traps, so there are confounding variables, but they are both well made and work well together. The Realtraps definitely look more "finished".
The tritraps are a little under 4 feet. Maybe 3'11" or so. You won't be able to stack two in the space you have so you can't cover the whole corner. Same for the mondo traps. Have you thought about the soffit traps? You can get them in custom sizes.
Tritraps seem like they are designed to be stacked from the floor up. There's no easy way to mount them on the wall, so that might be the deciding factor in itself.
Anyway, I'm sure the folks from Realtraps and GIK will stop by to help you out.