As Martin mentioned, we have sold
10Bar in the US probably longer than anyone. People tend to either be very happy with them, or not so happy...go figure ;-).
They are pretty rugged housings overall. Buttons are close together, but some are raised up. Other dial controls are a bit hard to engage, but work ok with some practice. They are a bit heavy in the water as well. As a good value they are hard to beat, but they just aren't designed/built to the standards that Nauticam uses.
Their support can be a bit problematic, that's why having a good dealer that works with them is a big help. They have recently hired another person for support and it has been getting better. But I still call them directly to get help for my customers as needed.
As far as the above corner issues with the 9-18, I haven't seen it when stopped down to f/8 or above when at 9mm; something that you really need to do with any housing.
I have a blog article comparing the 3 popular housings (10Bar, Oly, Nauticam) it's a little older, but the info is still valid.
See:
Purchasing a Mirrorless Camera System
BTW, we have one
10Bar E-PL5 housing in stock on sale; with an extra parts kit for only $899 right now. The
cameras are also on sale for $50 off.