Sodastream alternative CO2 sources?

Has anyone here used any of the various adapters for re-filling sodastream co2 cartridges?
For example, the stuff at http://www.co2doctor.com/productselector.htm

If so, any insight as to what you picked, and how well it works for you?

(My thoughts lean especially towards this: http://www.co2doctor.com/freedomoonespec.htm)

Thanks!