the R.S. spl meters are very popular;
if you want to check relative spl's (level diff. between different speakers), then it's good;

but if you want precision readings, then you have to pay more for a precise instrument that will give you true spl's.

modern AVR's are quite good in setting equal loudness on surround systems.

See: http://www.blu-ray.com/community/gallery.php?member=Gelli
or: Axiom Gallery