Matt;
Good post on the differences.
I grabbed a Fastrack railer a while back. It works great for the Little ones, they often have trouble getting the wheels lined up.
And it works great to impress newcomers to the layout. I have far more rolling stock than sidings at this point, so I'm always swapping out cars.
Pop the couplers open, set it on the railer and let go, they couple up nicely if you keep the consist pushed a bit over a car length away.
Even More impressive is if you set an engine to creep away and load the cars fast enough to catch the rear end of the train.
As for O guage re-railers, I may just build in a few, now that they are mentioned.
Seems like I've always got something derailed on a switch at the far side of the layout. Usually the lead wheels on a steam engine.
Doesn't matter where I stand, it's always the farthest one from me !