I haven't used one on my bike but I have one attached to my old Cadillac pretty much permanently when it's in the garage and it's been fine. The battery was already old when I imported the car 3 years ago and it's still going fine now, despite being far too small for the car! I think the maintenance mode is a quick pulse of 14-ish volts to keep the battery topped up.
I use a Ctek 3600 full time on the battery and I'm 18 months in on the current battery with no sign of problems so far. I use it from time to time on the car batteries too because it seems to have a bit more oomph with a very low voltage battery, although it takes ages to charge fully. IIRC they flash it with v quick high voltage spikes to reduce sulphation, but I could be wrong. The 3600 has a cold weather mode which I think uses a slightly higher voltage when charging (14.8V? Someone else might know....)
The CTEKs are great but the one to have is apparently the £180 quid one that can supposedly revive fairly knackered batteries with its clever sensing mode & voltage cycles. Seeing as I have four in my motorhome and four in other vehicles, plus one on the bike, I'm v tempted to get one.
And I've no idea why the Halfords one is so big and the CTEK so small..... I'd buy CTEK next time, just for the size and clever electrickery, but I'm not really sure what tangible benefit I'm getting!
