I owned a 2006 Mainship 34T a few years ago.
It is a great couples boat. But for more than two sleeping aboard, accomodations are limited. There is the pull out couch, but your guests are sleeping in the living room.
But if you are just a couple or have very occasional guests, the layout is great. The wide beam makes for a huge main salon. I like the galley down arrangement as it keeps the salon wide open. The forward queen berth is ok, but I would have liked some shelving along each side, but could be added. The flybridge is also huge, both it and the salon are helped by the very wide beam for this size boat- 14'. We had a cocktail cruise with 8 up there and felt safe and comfortable.
Engine access for the single is very good through the flip out stairs. This also keeps down noise in the main cabin.
The boat will cruise at 12 kts and 2,900 rpm burning 11 gph. Seakeeping is what you would expect for this kind of boat. Following seas make the boat do S turns with a simple autopilot due to the wide transom. Use a gyro autopilot to dampen it down to reasonable levels.
Some including me, have had problems with the ZF Mathers Microcommander electronic throttle/shift system. Mainship said a relay change will fix it. Others have pulled out the electronics and switched to cables.
That is really the only mechanical/electrical fault I have found.