Only tub-thumping again - but (sorry Terry) why use a tuner if there's an instrument present that can't conveniently be tuned, eg melodian or whistle.
A recorder can tune, but only downwards, and that puts it out of tune with itself. So the guitars (in this case) should have tuned to the recorder.
And ears are even more widely available and cheaper (till they go wrong) than electronic tuners. Why not use your ears??????