How old is your tank and what corals and stuff do you want to try and keep? The more difficult the livestock the more useful a meter may be. Problem folks have is that they adjust their spectrums later, add more blue and then what's the new par at?
This will work if you are adding "easy" corals, but knowing par can help
It helped exnisstech when he found out he was too low.
If you can borrow one locally, throw the lender a frag and then you will know.
I have one, rarely use it but I have let folks setting up a new tank borrow it and they snapped the probe wand. It's an expensive item to purchase for as often as I don't use it. Still, when I want to add a new coral I can have a PAR number instead of a guess. I had lived for a long time before I got one and probably didn't totally need it.
The Primes are common lights and you can probably look up outputs from others who have them and have a reasonable idea what your PAR range is likely to be.
