Hi, I've had my TVR1A for several years and no trouble at all. I haven't used it in a boat though, just ran it on air and steam once in a while.
I feel it is a very good engine (especially for the money). However it is not the ideal beginner engine (if you buy the kit version, which I did), because it is rather complicated to build and adjust. You mechanical skills will reflect in the running of the engine. And you need to make sure parts won't work loose and upset the timing. Loctite them in once you have found the right setting.
I also have to say that all kit parts fit very well, without any problems. After some running in on a drill, the engine ran very smooth and controllable.
Regarding twin oscillating engines: they are the closest a steam engine can get to "plug and play". Simple, reliable and well suited for beginners.