For me seems who uses battery tender, their batteries die ... . I never(Daytona 675 and now BB) used one(i bought it and still in box) and battery is ok.
I have 27k km on odo now, we have 5 month cold winter. I leave battery on bike and ca run bike 4 - 5 x 10 min during winter, thats all - it started without problems on spring.
So i don't see anypoint to use battery tender by myself or take battery off the bike .
Only the case when batteries(3x, before i checked voltage) were burnt by Dyatona 675 was when their famous voltage regulator failed and output voltage was over 25v, that was fixed by using aftermarket MOSFET voltage regulator.