Read up about using the 5L mini kegs... IME, they suck (hands down). They cannot withstand much pressure, so you need to be very careful about how you carbonate them. I DID use some for parts of two brews/batches. Due to trouble cleaning them, how they leak (CO2 and brew) and such, I never used them again.
IMO, better off saving the money trying to get those to work and put it towards real kegs.