(Edited my response because I think I missed the point after reading the question again...lol)
Everything I've tried that was small/mini resulted in headaches and problems. These included small setups using various gram sizes of disposable co2 cartridges.
My nano tank might not be as "nano" as some, but my final (headache free) co2 setup ended up being the same full size regulator I use on my other aquariums, except with a smaller cylinder. The most important component for me was a needle valve capable of the extremely low flow I wanted (I like the swagelok 21/22RS valves).
Everything I've tried that was small/mini resulted in headaches and problems. These included small setups using various gram sizes of disposable co2 cartridges.
My nano tank might not be as "nano" as some, but my final (headache free) co2 setup ended up being the same full size regulator I use on my other aquariums, except with a smaller cylinder. The most important component for me was a needle valve capable of the extremely low flow I wanted (I like the swagelok 21/22RS valves).