Personally I think they should be only allowed for low single figure golfers.
I don't appreciate being held up by a fellow high HC'er who spends 30-60 seconds "finding the pin" from 200 yards out....
Only to hack it 50 yards after all the fuss... Rinse and repeat from 150yards and on most holes.
Personally, I don't think it's my business to decide what is "allowed" for others to use and buy.
And, the only people I've ever seen take 30-60 seconds finding their distance weren't the ones with range finders....they were the ones without
So, alternatively, I don't appreciate being held up by a golfer without a rangefinder that can't find the yardage marker and decides to hit his 150 yard shot when he's actually 200 yards out....rinse and repeat (I'm not hacking on you, just demonstrating that the argument goes both ways.)
That said - I only found it useful once I had a bit of consistency hitting my short and medium approach distances within +/- 10 yards or so....and for larger distances, +/-25 (just for quicker club selection)
IMHO - use what you like, don't sweat other people's choices - it's none of my business what they use or not