Having one, I just don't see the benefits . . . I am one that loves bottle guns, but the Huben does not really need one. The tube is titanium, is a good size, and can take a 350bar fill if you can get it, and gives a ton of shots even on a "partial fill" on all but the most powerful tunes (and even then probably close to 30 shots). A big full bottle might give a few more shots, but it would make the gun larger and likely heavier too after fittings are considered, vs. the titanium tube.
I think it would only be a benefit for low pressure fills around 3200 psi or so. I usually fill mine to 3800 psi and can get almost five mags out of it (probably close to 90 shots or so), but I'm running mine at about 32 FPE.