If your garage walls are brick / breeze block then the finished effect is good.
It does take a long time though and the paint will just soak in to the walls.
If you've got plasterboard walls, job is a breeze and any slight scuffs / marks are be quickly touched up.
Please, please, please don't be tempted to paint your garage floor.
Despite what it may say on the tin and whatever preparation you may do in advance, the paint will always peel.
Looks great when first done, six / 12 months later looks patchy where it's peeled and you attempt to touch it up.
Oh, the slightest bit of water that you get on the floor will turn it into the slippest ice-rink you've ever been on.
My advice - get lino.
Works a treat and enables you to park your car and keep your garage looking lovely.
Above advice all learned the hard way !!