I have a few IMRC Gevo's of various colors, including some of the Heritage units. They are weighted well and are good pullers. IMRC adjusted start-up values and speed curves for the non-sound units to run with their sound units. Keep in mind that their non-sound units actually have a DCC decoder pre-installed in them. I don't have the info handy, but if you adjust a couple of CV values, all of these units, both sound and non-sound, will run well with every other model out there.
In regards to details, they are well done, however, there are some sever issues with the fuel tanks and side frames on these units.
Regards,
Russ