Hi,
personally for me it's curiosity and trying something new,
I have been "springing" for 10 years and have owned Weirach guns, cheap ones and BSA...
I want PCP for Jan next year unless wifey comes up trumps for Xmas (above) but the Co2 TH78D just interests me as its different, cheap and tunable (a bit like a car) and I like to tinker with things! If I break it, it's only £130 lost!
I know of no advantages apart from cost and maybe ease of refill in the field! Saying that PCP will normally hold more per charge than Co2.. Balenced eh?

Adam