I had 1993 intruder
Before I had the M50, I had a 1993 800 Intruder. For the most part, the intruders didn't change much through the years. With the now S50, most of the changes are cosmetic. Not alot in technical changes.
Now, for the differences between the M and Intruder/S50, the S50 will seem to have a little more HP to the road then the M's. It's a much lighter frame.
As mentioned, Intruders/S50's are not EFI.
There were a few things I did not like about the intruder, that I was adamant about not dealing with on a new bike. First and formost, the location of the battery on the Intruder/S50 is a pain in the arse. Second, narrow front tire, not as stable at higher speeds as the M, I actully had popped the tire off the bead of the rim and busted the innertube rim because it got trapped between two of the steel repair plates that were on a draw bridge. Spoked rims mean innertubes, an non radial tires. With the 1993's and probably some other years, I could not find a compatible maintenance free battery for it, and I was at one battery a year for the last 3 years I had it, and the dealer I traded it at had to replace the battery for the person who bought it. I had the electrical system diagnosed with no issues. So ends my rant about the intruders, but it was a great bike other then those things