I have a man strom and find the stock strom ergonomics more comfortable than the FJR. Will upgrade the seat sometime in the future, but leg room is awesome for my 5'11" and handlebars work just fine for me without modification, although some do upgrade those to reduce vibration etc which I have no issue with after TBS.
Passing power is plenty for a man strom but not quite the rocket that the FJR is. Speedometer accuracy however is sucky, use a GPS or a cyclometer. In the twisty bits the man strom is just as fast if not faster than the FJR in the tight stuff.
The FJR brakes are exceptional, strom lacks in brake feel and performance, but they are adequate. Man strom engine does have a slight chudder at low rpm but it no longer bothers me, just how the engine is.
Wind protection is not as good as the FJR obviously, lots more buffeting in stock configuration, but much improved with aftermarket bracket and laminar lip.
Both bikes are pretty much bullet proof, as for gas mileage the FJR has been more consistent mostly mid 40s but sometimes 40 when I push it, the strom on the other hand is high 30s to low 40s normally but drops to mid to low 30s when I whip it. Much more inconsistent. Despite this both have pretty good range due to a 6.6 gallon tank on the FJR and a 5.8 gallon tank on the strom.