R4M's were very small rockets with an explosive charge, with a trajectory similar to a MK108's 30mm round according to what I've read. It wasn't an airburst rocket like the WGr.21, however 1 or 2 hits from the weapon were enough to bring down a bomber.
They were generally used like a shotgun from 600-800 yards as Krusty suggested. Still extremely deadly weapons. And they didn't have the extremely heavy, draggy stovepipes that the WGr.21 requires.
I think the Me 262A-2 was capable of carrying a pair of WGr.21's, though...
Motherland is absolutely correct. R4M's would be absolutely devastating.

No cool launcher like a Dog Sabre, but nonetheless very effective.
I'd love to see an X-4 option as well. They were never operational (officially), never even tested on 262's, and I seriously doubt a 262 pilot could hit a damned thing with one, but it sure would be fun to try!