A friend of mine who works for the NM Railrunner Express says that there were a number of problems with the prototype DMU and trailer when they were in service on TriMet in Florida. Most of those problems, however, were due to the fact that these are prototype units, which will have some problems since nothing ever works as well in reality as on paper (that's why prototypes are built, after all, so the engineers can identify and correct problems before placing a product into full production) and that they weren't tailored to meet TriMet's specific needs. It's quite likely that the production versions will do better than the prototype units, but no one will know for sure until they've been in service for a while.