RainmanP

Velo,
I think I have the Ultraflate. It gives you the option of using threaded or unthreaded cartridges. If you want to go ultra-light you can carry just the head and a threaded cartridge. I think the Microflate is basically just the head part of the Ultraflate. For most riding you carry the head and body with an unthreaded cartridge or 2 (as a commuter I keep about 4 in my seat bag 'cause ya never know). You can buy the unthreaded cartridges in boxes of 25 for about $9 at Wal-Mart with the bb gun stuff. The threaded cartridges cost quite a bit, like a couple of bucks each. I have never had any trouble using mine. It works on presta or schrader. For presta you just push it on and pull the trigger. For schrader you screw the head on the valve then pull the trigger. Inflates a 700x23 in about 3 seconds - lots faster than any pump. One caveat. I have read that when you get home you should let the CO2 out of your tire and pump it up with a regular pump. Something about the CO2 maybe affecting certain types of tubes. I don't know for sure, but I do it anyway since in only takes a couple of minutes and doesn't happen often anyway. Also, it's probably not a good idea to carry the inflator with a cartridge installed. For one thing the gas may bleed out, for another there is no "safety" so it is easy for the trigger to accidentally activate, wasting gas and possibly causing minor injury.
FWIW,
Raymond