i've been using m1 20-50 for 4-5 years now, my friends bike uses it also. no problems whatsoever.
mine 2k I/S, his 99 I/S, loaded on 3-4 thousand mile trips sea level to colorado.
i like it.
i also run mine kinda hard when momma's not on back.

also 29,000 on friend bike 36,000 on mine.
i know............not even broke in yet LOL