I have the Growler saver. It works good for me. It works best with the 64 oz grolwler as keeping the 128 oz pressurized after the're half way empty can run you through a lot of CO2 capsules. http://www.beeradvocate.com/community/threads/growler-saver-vs-tapit-cap-thoughts.84802/
I could be wrong but I believe Growler saver is out of business. Their websites goes to a 404 error and they haven't responded to facebook or kickstarter queries in months.
I have a DrinkTanks 64oz and the CO2 system works as advertised, but you do have to create headspace which means less than 4 full pints dispensed. Also the external manual injection of the CO2 isn't as elegant as the design on the GrowlerWerks uKeg.
I find that regular growlers do pretty well in general. I always give the tops an extra twist or 2 when I get them. I have kept growlers for over a year with no noticeable carbonation loss. This particular one was a barrel aged Dubbel, so I wasn;t as worried about oxidation from the filling, but this brewery does it as well as possible - CO2 flush, sealed fill and so forth. For homebrew, I have other caps I use. I don't know what they're called offhand, but they are heavy plastic with a sort of cone inside that seals better than standard thin metal ones.
