I haven't got his black paints as I haven't had a real need yet. I do have some colors that aren't on his site anymore, and most recently got the ek blue. It's very matte, exactly what I hoped for when I ordered it lol.

I love how smooth his paints are, and I've never had to go over again for better coverage or deeper color. Worth the price imo, and I like the idea that buying from him helps fund the next wild thing he comes up with

Black 3.0 is a good, all around ultra-black. It is certainly a bit lighter than 4.0, but also applies differently, 4.0 almost needs some muscle applying, it is very thick and sticky. I think they're both identically priced, so I'd say the difference is really how you'll handle it, and in the final mechanical properties, which apparently are slightly different, with 4.0 drying a bit less resistant than 3.0.

If you want an even blacker black, consider Musou Black, a Japanese ultra-black. Can be airbrushed, too. Not saying 3.0 or 4.0 can't be airbrushed, but I imagine 4.0 will take some fiddling around.