C02 is fine for a single shot. Like John mentions, the CO2 gas phase is temperature sensitive, also rapid cycling of the valve in a CO2 repeater can exhaust the gas in the reservoir by outrunning the rate of gas conversion, causing pressure drops - this is one factor that affects the paintball shooters. But if you're shooting slowly, you should be fine even at lower temperatures.
The big complaint w/ the older CO2 match guns was that the velocity would drop sharply as the reservoir was depleted - i.e. they don't have a linear pressure curve like gaseous NO2.
I'm sure that that's just a prototype depicted - it looks pretty rough. But PCE has a good rep in the shooting community. I'm sure that the final product will be top notch.
* Scott's post on targettalk mentions that these had been developed in support of a new CMP event. It may be that CO2 was chosen to keep costs down.