Yes I have one I use with my Mark V. I was using a Bogner OS212 which sounds great...but I wanted a smaller open back 1x12cab as an alternative.
The speaker was a bit harsh and hard to dial in for the first 1- 3 days. esp compared to my well broken in 212....but then it just smoothed out and sounds really good for all types of tones from clean to mean. What I really like about it is how when you place it a foot or so away from a wall, the sound coming out the back just starts to bloom around you. Makes it so much less directional as well as less "in your face" when you are right in front of it ( as a closed back can be). As a result it sounds much bigger than it really is ...lord knows I really hate trying to play rock though a boxy small 1 x 12.
I havent gigged it yet ..but this is the box to bring on the small room , un mic'ed gigs.
I dont find myself missing the second speaker nor do I miss the slight drop in the "thump" factor I get with my 412 Rect cab or Bogner 212.
Hope that helps