I made a new mount from scratch welded to to standard 21 front frame, along with an RGV idiot light panel. The speedo is perfect and easy to read, though the tacho is slightly less visible though the rpm warning lights which are easier to spot.
Fitting can be fiddly with all the small wires to connect to certain points in the loom, and chances are the speedo wire will need shortening (which is hard with such tiny wires)... I had my loom apart at the time, so it wasn't too much hassle, but otherwise, if you're a competant solderer, then you'll find it logical and easy enough.
Overall I'd recomend it, though it was the best option in my circumstances (Yamaha engine won't work with NSR tacho, no speedo drive etc), but if I owned a 'normal' NSR I think I'd prefer to keep the stock clocks.