I agree with Michael here. A boom brake just isn't necessary on the R22.  
Then again, I've always been accused of being a charter member of the KISS  
society. I like to keep things simple and uncluttered. To many things to deal  with 
can really hamper your ability to deal with a crisis when it shows up at  the 
worst possible moment.....and believe me, I've had a few pop up from time to  
time.
Now, that being said, when going down wind wing on wing, a preventer can be  
really nice, but that's a whole different animal and easily done with a spare  
line and a little imagination.
 
 
Rummy