The BCM, DCM, and SRS systems are only gotten with the more expensive scanners - that said, the expense is more the software than the hardware. It is rumored that the cheap, Chinese scanners can do most of what the $5k plus scanners can do - but keep firmly in mind that the difference between validated and buying a new computer is generally wrapped up in the price... Quite frankly, you'd be better off throwing $100 at your local mechanic (who is paying off the snap-on $7,500 scanner) then you would buying a cheap, Chinese scanner. I'm sure there are people that are lucky and don't have problems - honestly, I wouldn't risk it.... especially since they may have to program a new computer for you once the diagnosis is complete.
The experience comes because my SRS computer died (it thought my rig had rolled when it hadn't). It require a new VIN burned into a new chip. One other thing, when you pay a mechanic to diagnose, you get (the good mechanics) a person standing behind their work - with my SRS, it went from solid fault to intermittent fault (which was probably the cause of the original failure)... he had to go through and clean every pin in the SRS system to get the codes to stop - all of which, didn't cost me anything more because he and I bought understood that the computer may not have been bad.... I'll tell you what, that was a breathtaking amount of work he did for free....
Point is, you may be saving pennies to spend dollars.