The Alfa will take bulk fill and is supplied with a 150gm bottle and adaptor. IMO you are better off with 12gm capsules though as it is difficult to tell how much gas you are transferring from bulk. A 12 gm capsule gives 80 - 110 shots depending on temperature and velocity setting.
The Alfa is a pretty good gun, but with the present price of £320 new, I think you would be better off with a good S/H Aeron or Tau, probably for less money. When I bought my Alfa just over two years ago, it was Euro230 delivered, inc VAT. A different ball game.
A shooting buddy in our club got an excellent Aeron for £150 a few months ago. No-one seems to want CO2 any more, but that's their loss! Flavour of the month syndrome maybe?
Walther CP-2 Match, FAS 604 & Tau 7 target pistols, Smith & Wesson 6" & 4" co2 pistol, Crosman 1377,
Baikal IZH 53 pistol, Gamo CFX Royal,177, Umarex SA-10 CO2 pistol.