Produced at the end of the M2 product cycle as Leica was already switching to the M4, the M2-R was basically U.S. Military surplus sold to civilian consumers.
In the 1960's the U.S. Military contracted with Leica to make a modified M2 that utilized the M4 style rapid film load and some added body sealing. The numbers I found say they took delivery of something like 875 units. Internal to Leica it was referred to as the M2S but was marked as an M2. The military designation was the KS15-4. But it seems there were no outward designations (other than asset tags) to signify that is was different than a civilian M2. There are reports of people buying what they thought were M2 retrofitted with the M4 film loader only to discover they had a M2S, nice.
At some point the the U.S. Military canceled the order for the remaining M2S (presumable in favor of the M4M, M4Mot and KE-7). That left Leica with parts in inventory. So in 1969 and 1970 they produced 2,000 unites designated M2-R and sold them to the consumer market.
What is not to like about the M2-R? You get build the quilty from the best of Leica. You get the frame lines and viewfinder of an M2 and the film loading of an M4. Plus you get some "military spec." added body sealing. Don't ask me to identify where the added sealing is or how much in help, just sounds cool to say "military spec.". If that is not enough it has an extra letter in the serial number so line up Leica collectors.
I already like the looks of the M2 over the M3 and the M2-R added the benefit of the M4 film loading. I used the Summicron 35mm lens because the M2 line has the added advantage of 35mm frame lines, unlike the M3. Mine is in very nice shape and preformed like a champ.
Is the M2-R better than a standard M2? That depends. If you just can't take the M3, M2 style drop out film spool: the M2-R is a solution (but so is an M4). If you are a collector, the M2-R is a nice find with an interesting history and low production. If you want a great Leica M with the added upside of a collectible, a nice option. If all you want is am M2 as a shooter and can live with the drop out film spool, save your cash. But if you are given the choice of am M2-R at an M2 price, hand over the money and enjoy.
Lens: Leica Summicron-M ASPH. 35mm f2.0
Film: Ilford HP4 400