Have owned a Roni for a year, used first in my G19 and now in my G17. We had a Roni match last Friday, running an IPSC-style stage with two 32-round mags. Fun, fun, fun.
The Roni was developed as a niche product for markets in which pistols are less regulated than long guns, and where guns are regulated to death anyway. They are fun to shoot and hang things off, afford a very high practical rate of fire with good accuracy, but the effective range is still that of a handgun.
Here's a nice video of the stage in our match: 11 steel plates and 12 paper targets (triple taps).
http://youtu.be/xGkumwez5Mc
If I lived in the U.S., I would probably steer away from the conversion kit for civilian range use, due to the NFA hassle, unless they get an ATF letter stating that muzzle attachments that give a 16" effective barrel length make the Roni a non-SBR. But here in Israel, it's the best fun an ordinary citizen can have with a service pistol.