=>Are these Bachmann motors really better?
Yes. The old ringfield motors have relatively weak magnets, and are power hogs. Modern motors use 50% or less of the power of those old motors. Also, manufacturing tolerances have improved - all modern motors and gear-trains are better than those 20+ year old ones (this is an effect of computer use in manufacturing.) Result is much smoother running.
=>What is the purpose of the flywheel?
To help the engine continue moving over brief interruptions of power caused caused by dirty or oxidised track. Works.
=>Do Hornby and Lima also use this motor type?
Lima does. Hornby AFAIK has also moved to the modern motor-gear train combinations. (Sorry, I avoid Hornby, except for old stuff that touches my nostalgia nerve. Hornby have been coasting on their half-century old reputation, though there are signs they have awoken to the fact that the expected standard has risen considerably.) Lima however has below average mechanisms - the effect of trying to meet a low price point -- electric trains are "toys" after all, and many people balk at paying precision mechanism prices for them. BTW, Lima has declared bankruptcy, and may not be resuscitated.
=>How long have Bachmann (and Lima/Hornby if applicable) been using this motor =>type, since if you buy secondhand on eBay or by mailorder it is not always =>possible to tell that's inside the body...?
If you want to know about the mechanism, ask, or insist on return rights if not satisfied. There's no point buying stuff that disappoints. AFAIK, _only_ Hornby ever used the ringfield motor. It was an attempt to increase motor efficiency given the weak magnets available at the time. Worked well, but has been surpassed. BTW, many so-called "can motors" use a ringfield, too.
=>Thanks in advance, =>Steve.
Get your trains up and running, and then replace the locos or upgrade their mechanisms as time, talent and cash permit. Many of the old locos will no doubt end up on the display shelf -- I have a soft spot for old Hornby myself, but don't run any of it anymore. :-)