Been offered a bike from a friend of a friend with one for the first di2 incarnations (2011?) on it for a reasonable price.
Apparently, the bike has not been used much (if at all), but I’m concerned about buying a bike with an 8/9 year old electronic groupset on it (if it were mechanical, I’d buy it no question).
Anything to particularly look out for with old (infrequently used) electronic groupsets? Was the first di2 even any good?
Thanks!!
I wouldn’t bother to be honest. Di2 has come far since then. I had two bikes with the original Di2 and the generation after, and after about 2 and half years both started to have issues. Generally connection issues in the shifters and junction boxes which meant sometimes the gears would stop working and I would have to push the cables back into the ports after they came loose. Far from ideal.
Granted both of these bikes were heavily used, one started developing problems after about 16000km and the other at about 20000km.
Agree with Janerney, even if they do work fine you’ll have difficulty sourcing spare parts! And doubt any recent shimano Di2 would be compatible. Save extra towards Ultegra Di2 6870 
If the cost of the Di2 seems to only add a 100 bucks or so to the bike than take it for a ride.
Just think of it as ‘buying a bike’ rather than buying the groupset, don’t buy it because of Di2.
A friend has the early Di2, he had to buy a new rear mech, difficult and expensive. Plus you’ll have to factor in that you will have to buy a new battery if it hasn’t been kept topped up.