My OPINION - I haven't had the opportunity/need to run or repair one.

I see the following as potential drawbacks to the gen-set concept for most railroads:

1. Requires a railroad to stock additional parts, tools and have to train maintenance personnel. (Remember when railroads had to maintain EMD, Alco, Baldwin, GE and F-M?) Many of the parts are unique to the builder without a third-party source.
2. These are heavy "truck" engines, and have a much shorter overhaul interval than an EMD or GE. I suspect that owners will have their arms twisted to repower them with cleaner engines each time rather than rebuild them.
3. These have an unneccesary amount of complication - lots of electronic units. Each order seems to have subtle differences. When the electronics eventually fail, will replacement hardware and software be available?
4. The chopper and other propulsion control systems in use introduce additional power losses. I have not seen anyone state if these losses are minor or not.
5. I know that NRE's gen-sets operate based on throttle position. The higher the throttle position, the more engines on-line. The inherent delay in starting the second (or third) engine does not allow full power to always be available compared to a single-engine design.
6. The constant cycling of engines causes additional issues - failed starters, etc.
7. Part of the performance issues may be linked to software restrictions intended to promote fuel economy.
8. I did ask a former UP machinist what he thought. He mentioned it took more effort to service them due to having multiple engines.

Past history has proven that if railroaders (either the crews running or maintining them) truly don't like them, they will abuse them to the point of failure hoping to get something better.

Time will tell ...