Actually on the throttle grip I am using the Throttle Rocker, which I find more comfortable because it is thinner and has a more contoured shape...
+1 - This is the exact unit I use on the FJR with stock grips. It is a "
Throttle Rocker" brand. Unfortunately, it also seems to be unobtanium now, as the "new" velcro version has taken over. I have one of those also (mounted on the VFR) and much prefer the original for it's ultra easy adjustability.
The key is keeping it adjusted so the the throttle can be released with only a slight dorsifexion of the wrist and raising of the elbows a bit. When cruising you do not want your wrist to be completely straight, it will need to be slightly flexed and you need to get into the (good) habit of dropping your elbows and not straight arming the bars, or you won't be able to release the throttle fully when it's time.
I also find that with certain jackets, the bulky sleeves require an adjustment to the rocker to allow the right range. One jacket in particular I allow the TR to slip between the cuff of the jacket and my wrist while riding as it gives me a better feel. That's what makes the first gen TRs so nice, since you just spin it around the grip once to the new position you want it on the fly.
Probably the most important thing is getting used to it being there, if you haven't been using one before. Once you are used to it it gets tough not to have. I had taken mine off to use on my Trophy a while ago and forgot to swap it back (which takes literally seconds) before leaving on a 10 hour ride on Sunday. My right arm was pretty darned tired by the end of the day because I'm not used to having to grip the throttle so tightly.