I found that the Co2 came in spurts a little bit more, but the output I believe is roughly the same. The check valve tends to wait until a level of pressure is built up, then the valve opens and shoots out some more co2.. It then waits for the build up again, but it doesn't take long.
I would definately recommend it. I had not done the top up quite enough, and the tubing then started to syphon the water from my tank back into the cannister, then dribbled out onto the floor. I must have had a few bucket loads of water spreading across the carpet in the lounge before i noticed, so for me it's a must.
Hope that helps.
Squid