There are three models. They are the Motor Drive E, the Motor Winder E (usually called Motor Winder E-I), and the Motor E-II, also called the Ei-II. Look here for descriptions:
www.tamron-usa.com/bronica/etr_guide.asp
The Motor Drive E was made from 1976 to 1988. It the biggest, heaviest and slowest. It can take remote control and external power, though finding the accessories is probably difficult. As they are bigger and heavier, and all very old now, I would not buy one.
The Motor Winder E (E-I) was made from 1988 to 1998. It is shorter, lighter and faster, but does not take remote control or external power. It can be triggered by standard cable release, so it can be remote controlled in that sense. It is the one I have, as it is about half the price of the Motor Winder E-II and serves my needs well enough (mostly tripod mounted macro). I'm thinking of selling it, as I think I would rather not have its weight and bulk, and the wind crank is just as fast.
The Motor Winder E-II was made from 1998 to 2004. It is much smaller and is lighter than the other two. It takes remote control and external power. It has the batteries and motor in the handle, so it is about the same size as the Speed Grip. It is worth the extra cost if you are hand holding the camera or need the extra features the E-I does not have. From what I've observed it costs about $100 more here in the US than the E-I and considering that it is newer and more advanced it is worth it. Its only drawback is it does not take AA batteries, as you won't find 2CR5 batteries everywhere, and they are more expensive. But it takes only one, so it's easy to carry a spare.
As for Speed Grip vs. Motor Winder, I think it is usually better to use the Speed Grip. It is quiet (which the winders are not), less expensive, lighter, and of course needs no batteries. It requires two strokes, the first a full stroke and the second a little less, but I find it is fast enough for me. I can match the 8/10 second of my winder if I try, though I usually take about 1.5 to 2 seconds. If I were doing a lot of shooting in a short time like weddings I would use a motor winder, to keep my thumb from getting sore and to gain a little speed.