If he has the filter in there he should be OK but I would much rather use compressed air.

thanks for the advice - i'll let him know

I actually ran CO2 with a remote on mu Impy and no issues at all. Gun shot great air was consistant. Never put it direct to the gun, but remote all day.

That is a very bold statement, everyone has a different opinion, read the users guide says you can, all personal choice.

Cost more, highly inconsistent FPS/pressure and it destroys o-rings all the time. I see zero reason for anyone to be running CO2 anymore regardless what type of gun you're using. You can get alum. 47ci tanks for under $50 bucks and at my local paintball store it's $5.00 to fill my scuba that my dad, brother and myself play off all day long and have never run out of air. You can buy scubas for under $150 brand new and get used ones for less than that. If you have a local place that can cert them look for ones that are out of date or almost and pay the $20 to get it cert but get a huge discount when buying used. FYI, don't take a tank to a paintball/scuba shop to get cert unless you want to pay them the middle man fee for doing so.

Just so nobody is confused or turned off of HPA. A good majority of scuba shops for some reason want to see a dive card to fill you tank. This is not a law or requirement, just some chip on their shoulder. I'm not sure of state to state regulations but I'd be interested to see the actual law ordinance and I think it would also be good info for others in that state as well. In AZ you need no such thing but as mentioned you will get a bad attitude from dive shops. I'm lucky enough to have the largest and best paintball store in the whole state 2 miles from my house but for those that don't also check out welding shops. I only play woods ball myself and have never drained my whole scuba with 3 people playing off it. Yes CO2 gets more per volume but wait till it's 40 degrees out and you rip some balls. I don't care what you have for a gun/reg, your world will be sucking quickly!! Also, accuracy is directly linked to consistency. You'll get neither from CO2 during the course of a day. I know your accuracy isn't going to be a huge diff but ball on ball at 100ft is not going to happen when your fps varies 50fps. Just my pref, not saying you can't or absolutely shouldn't. My argument is don't put a dime of money into a CO2 setup!

Bottom line - there are pro's and con's to both.  If you play a field that doesnt fill HPA, you are stuck with CO2.  CO2 can be used effectively in an Imp with the AS tube and the Maxflo.  

Would I use it now?  No.  I have already invested in a HPA tank.  I also have the money to do that.  Some dont, and the $20 (liberal figure - I know some are less) 20oz. pre-filled CO2 tank from wally world is a better option for some.  

In regards to Scuba filling - I don't believe there is a law in any state that requires a certification card for filling a tank.  However, a smart shop owner would not do it, just for liability reasons.  The "chip on their shoulder" you refer to BAD BOY is for a damn good reason.  He has no idea whether you are playing paintball or going diving without being certified, and he also has no idea as to whether you know how to operate your equipment properly.  It only takes one moron to sue you out of your livelyhood these days because they were irresponsible.  I have been a certified scuba diver for over 20 years, and every shop I go to requires a c-card for fills.  I have seen kids bring tanks in who were using them to fill paintball tanks and the owner or employee refuse them.  So depending on the shop's owner, you might not have the option to fill a tank, unless you dive as well.  They are protecting themselves.

The gases themselves - True HPA is stable pressure wise where CO2 fluctuates.  Personally, I have never played in temperatures where I have had CO2 give me any problems.  I used to use it all the time in the first guns I had (that was all that was available at the time).  And as far as CO2 being a dirty gas - Unless the field you play at has invested in a filter (mucho expensive!), I assure you, you really don't want to see what comes out of those bulk HPA tanks sometimes......

As I said - Pros and cons to both.