Can't speak to the Elmars on an RD-1, but w/ film the older versions (both 3.5 and 2.8) have more contrast than the Summar/Summitar, while also being quite sharp. They also tend to flare less than other Leitz lenses of the same era. If you like a Tessar, an Elmar is quite similar. Those features, and compactness, make them a nice daylight shooting lens for street or landscapes. The v.1 50/2.8 makes a nice all-'round 50 if you like lower contrast than a modern 50. The little 3.5, while ergonimically lousy, produces nice images in bw that have an older look to them. So, for someone like me who shoots in the bright sunlight of California, an Elmar works well as a compact 50. There are a couple of flickr groups devoted to the Elmar, so you can see for yourself.
The modern Elmar-M is often described as super contrasty and sharper than a Summicron. There are some members on the forum here who have taken some memorable photos w/ it.