All of the plastic 3rd rail diesels share a common heritage. Same basic drive. The sound systems are Lionel Railsounds originally as I recall, but that has changed with the last few projects. The big difference is the driveshafts in the original E7s were plastic, but there are parts to upgrade that. It terms of running, they are stellar runners for people who like more prototypical speeds. They are geared to only run around 60 sphm at top speed. The ball bearings on the axles for the last two projects make the drive exceptional.
The brass GE Dash 9 has a different drive system and really can't be compared to what is under the "hood" now.