First of all, what year or years are you looking for?  From their inception in 1947 (I own one of these) to about the mid-sixties, these machines have evolved quite a bit.  The first ones were about as graceful as an improperly loaded washing machine--you pressed the return and it would skitter to the right about three inches (they hit pretty hard).  I would say they got softer in this regard along about 1956.  From then to about in the mid-sixties, Underwood electrics were fine typweriters.  The main issues I had with the Documentors and Scriptors was that the little round keys were too small and placed too far apart for my big ol' fingers.  I usually hit two keys at once and was all the time un-jamming keys.  Also, the backspace pawls wear out.  You can reach these fairly easy.  Occasionally, I would take one out and resurface it with a Dremel tool and grinding bit.  Also, these typewriters' motors were a bit small, and there has been more than one time I would have to remotor it.  Usually, a bigger motor out of an old Remington 25 would be perfect.  All I'd have to do is to take the end bells off the motor, place them on opposite ends of the middle piece to make the motor turn the opposite direction, put the Underwood's belt pulley back on and Voila!! No more motor problems!!  Don't even touch the Underwood 700 or the 702.  Oh these looked handsome enough, but that's where it ends.  Unless you know how to change out the rotten plastic cam actuators on all the key levers (which all have to be removed for this operation) for metal ones, say, off of a parts Documentor or Scriptor machine, and put it all back together again, you'll be sorry.  Also, these have tiny little motors.  I remember having done all the above with one of these.  I got a fairly decent typewriter out of it, but it is alot of work.  You'd have to get one of these very cheaply and know a lot about removing and reinstalling key levers to make it worthwhile.  I hope I helped out some.  This wasn't any formal training I took.  This was just good old-fashioned experience I've had over 35 years of tearing stuff up in a million different ways, and I've got the scarred hands to prove it.