I've used the Boots own ones too and think they're brilliant - I found trying to put gel into lo's mouth was a nightmare as it'd never end up in the right place or still be on my (bitten) finger when I took it back out, the powders you just tip in (or give on a spoon) - and they're better if you're not sure where the teething pain is too.
Yes it's fine to give calpol with them, my HV always said so.
