Another brand to consider for value is NorPro. Good electrical end; primarily Yanmar engines; many happy users in the Hatteras community, no direct experience myself. At one point I was in the market for a second "night" generator of about this size and after a bunch of research and talking to folks, had it boiled down to NorPro or Onan (very quiet, lots of service outlets, other genset is an Onan). Since we were cruising extensively, having engines and gen-ends with good networks was important.
You bring up some good points.
Norpro is what we generally refer to as a "packager", in that they put together generators from off the shelf components.
A generator is nothing more than a prime mover (engine) governed at a specific RPM coupled to a generator end.
You can evaluate a "generator" by examining its components.
1. Engine... This part is easy because there are only a few engines being used for small generators. Yanmar, Kubota, Isuzu are a few brands.
The engine is governed in RPM by the governor. Generally in small generators this is a factory supplied unit that is part of the injection pump. It can also be a bolt on electronic unit which provides better frequency regulation.
The challenge with marine generators isn't the engine, its the equipment used to marinize it. This comprises of generally a heat exchanger, possibly a liquid cooled exhaust manifold, seawater injection elbow, and seawater pump.
These cooling systems are what you are probably going to need parts for. This is where to be careful with generator companies. The cooling system probably has special hoses with specific bends, things like that. Sourcing these kind of parts when you need them might be problematic. Also remember that the reliability of these systems is often dependent on the engineering put into them. Small companies do not have real R&D departments. This can lead to reliability problems
2. Generator End... Generator ends are simple in theory. Spin it at its rated rpm and it makes power. The problem is that generator ends represent a huge part of the cost of a generator and packagers are always trying to find a less expensive generator end in order to stay competitive.
All generator ends make power, but if you look at the components you will find huge differences. Brand names to look for are Marathon, Stanford Newage, and to a lesser extent Leroy Sommer. Marathon is based out of the US, and parts are available world wide. Newage is based out of the UK, and I've found that parts are readily available. Leroy Somer is a Emerson company but they have a pretty small market share. I cant vouch for or against Leroy Somer parts wise.
Other brands of generator end of course exist, such as Syncro out of Italy and several China based manufacturers, but be careful of long term parts support.
As far as technology generator ends are regulated by one of several methods. The best is electronic voltage regulation. This is what all industrial generators use. Then there is transformer based regulation. This is an older technology. Not nearly as accurate as electronic, but very simple and reliable. (lots of Westerbeke generators use transformer regulation). Last is capacitor regulation. Stay away from this. The capacitors tend to go out making you scrounge for parts. Also and this goes without saying stay away from any generator end that uses brushes. As an industry we got away from brush type generator ends in the late 70's.
The lesson here that I hope to deliver is that while small packagers can save money and make a good product, you as the purchaser need to examine what you are buying, because quality varies. Also consider where you will find parts if your packager either discontinues support, or goes under. Remember that a generator is a 20 + year investment.