within the finnish climbing guide they were used to grade everything from 2m boulder problems to 30m+ trade routes.
Finnish route grades and bouldering grades are not the same, they just look the same. But just wait to you've been spanked by a boulder problem that claims to be 4+. Just to add to the amusement, Finnish bouldering grades (Helsinki) seem to differ quite a lot from Finnish bouldering grades (Turku) - but they speak funny over there anyway so who cares
Until you can climb something worthy of Font grade (don't expect I ever will), with bouldering I would stick to the grades "can", can't" and "might in a few months". Alternatively ignore the actual problems and give grades to comedy value of friends' attempts at the problems - humerous facial expression or landing on your arse gets you an extra grade...
More seriously french grades for all sports routes does seem sensible - but it does mean that as some one else pointed out you will have two systems on one cliff as virtually all cliffs have a mix of route types.