If these are the 5L cans with a vent on top and a tap on the bottom, I've used them before. You don't need much sugar to prime, and they work well for the cask style, especially. I used to use them a lot before I got corny kegs. If you can get them for free, I'd experiment with them. The only drawback is that you need to finish it off fairly quickly, as they'll lose carbonation pretty fast. (That's why the "cask ale" style is good for them.)
Monk