They're a PAIN! I did some setups for the local science museum and all their tanks were in the wall. Not only are they hard to work on if you don't get enough room behind them it's really hard to get a sense of what you're doing when designing and pruning. It's a constant go around the wall and look, go back around the wall and trim/plant, go back around to the front, go around back...blah blah blah.
Aesthetically I think they're really neat once everything's done, but the working can be a problem.