Yes did it on my 620 (couple of years ago) must pop the top and have a look (it has done over 70,000km road since it was done) and this was an air cooled engine - from memory was meant to make engine cooler (my air cooled show +150C at EC in summer) and also add a bit of compression (we were shaving heads etc)
As for easy ... yes sent them off (well Gowanlochs did) and then they came back minus some of my money :(
I guess the effectiveness is up to the person talking ... I can't say if it helped my engine as we did so much but it was a great little motor at the time
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