Yup, not used one myself but know several people who've used those. Not heard any bad reports on them.
I have heard a few inc myself,
they can mask faults when left over winter,
my kawi battery was showing ok on the optimiser and started the bike, ,,
however when I tried again it was flat, good job I didn't set off anywhere,
tried it again, after an hour the optimiser said ok, yet after 1 start it was nearly flat again,
I have heard this a few times through friends and the internet,
theres cheaper unbranded chargers that do the same trick, great if you cant get to the battery easy, or cant be arsed in winter, but check the battery over properly before using...
i just use a normal charger now, and do it the old tried and trusted way , (remove battery, keep warm, discharge and recharge every few months)always seems to work,,,
i noticed the optimate doesn't like moped size batterys often either, just sits there with the lights flashing....my mates does the same