Do I need a trimmer with a hair vacuum or 'mess collector'?

Only if you trim away from a sink. Philips' beard styler models with the hair collector (the BT5775 5000 series and BT7670 7000 series) reduce countertop cleanup, but specialist reviewers note the collector adds bulk and doesn't catch every clipping. If you trim in the shower or over a basin, a standard waterproof trimmer is usually simpler.