I use this product sparingly due to the fairly high cost in comparison to the benefits derived.
This product is in my opinion the best in it's class of nitric oxide products. APS don't mess around and whenever they attach their name to something, you know it's going to do the job.
I take 7 caps (they recommend 6-8), so in a bottle of 90 caps, you can see why I use it sparingly. Use it on days that require critical results, like smashing a personal best for weight lifted.
It will increase blood flow which will deliver more nutrients to your muscles. You can feel it in the 'pump' you get from lifting. If you really want to test this stuff out, isolate a small muscle group like say biceps by doing heavy preacher curls and you'll feel an insane pump. I've also noticed a slight increase of around 5% in strength while lifting heavy weights.
If money isn't an issue take it prior each workout and stack this stuff with Mesamorph. If it's a luxury, like it is to me, take it on big muscle group workout days - back & chest, Legs. If you're looking to buy the one supplement that will help you build your body, buy some protein powder instead.