Did a quick test and it is a lot better than some because it isn't too strong a suction which means you get to clean more of the substrate before your water amount is up "this is down to the check valve and strainer" but as play sand is very fine you do get a little in the bucket of syphoned water you will get this with most so guess it is a trial and error until you get the hang of it
I took the vac end off the one I had and bought a Marina Siphon Start (the biorb one comes with a bulb at the end which is handy). I startt the siphon off, swirl the tube around above the sand and the grot that sits on the top gets sucked up. Any sand that gets sucked up gets sieved back into the tank with the new water, which means I can pull out MTS's and move them around to other tanks if I need to.
I should add that the Rena vac is excellent for most tanks but especially larger tanks as the tube length can be adjusted it also has adapters which you can connect to a hose to use in the drain outside, handy when doing larger water changes and certainly makes life so much easier