the only plus point of these is when you get a tune and you might want to know the bpm.
but i mean, most producers use the same bpm everytime they do a tune, so you always roughly know where to pitch it in relation to other tunes when you're mixing, eg
dillinja - 172
tc - 173
almost all other producers go off around 174
g dub/taxman/jayden/hazard - 175
clipz/die - 176
modified motion - 178
hazard does a few at 180
you get the idea.
but as for using one when mixing, pointless. but as a bit of homework when you get your tunes, it can help i guess.