As Philip (AzFishKid) said, you can use an inline bubble counter. Depending on your method of diffusion, you may not see much benefit. I find I really need one with my inline atomic reactor since I cannot see it working. If you use a reactor, which is possible with any CO2 setup I can think of, you could make it out clear PVC or buy a clear one so you can see the bubbles and therefore not need a bubble counter. Or you can make/buy an inline one.
Basically, you can use a bubble counter and a reactor on this, and other co2 systems, even if they are a complete kit. The regulator (not just this, any regulator) doesn't prevent you from using a reactor or inline bubble counter what so ever.
I know figuring out co2 is hard and don't mean to come off harshly, I just am trying to be thorough so you can make the right choice for your self.
I will say that I am very impressed by my atomic diffuser however. Never used a reactor but this is the best diffuser I have owned and being inline is a big perk as well. I don't like the actual look of the in tank ones compared to other options however which kind of matters to me so I don't know if I would buy the in tank ones, even though I know they work better than others I have used, I would just up the co2.