I just bought this kit myself! I read that that big ugly diffuser is one of the only ones that results in 100% co2 diffusion. I wish I still had the link to where I saw that, can anyone else comment on the accuracy of that statement?
To answer your question though I see no reason why you cannot use the diffuser you mentioned, however if you are taking that rout I think you will need a bubble counter and a better valve to more consistently regulate flow, however I am pretty new to co2 myself. On a side note I've heard that for a more natural look you can modify a piece of porous volcanic rock into a diffuser.
I have a question about this kit myself though; it uses 20g threaded cartridges, and I hear that 16g cartridges will fit it, but neither seem like a very economic option long term, does anyone know what kind of threading adapter would be necessary to attach a larger co2 tank?