It would seem that with your biking background and what you seem to be wanting to try on the trails, the P2 would be a good choice for you to break into mtb-ing. It is an entry level DH/FR/DJ type of bike that may have some questionable components should one try huge drops and jumps-namely wheels and fork.
That said, it is pretty important that the bike fits you and serves the riding style you are interested in. If you are interested in some XC or All Mountain, perhaps an AM bike might be a worthy consideration. For XC, the P2 might be heavier than XC hardtails. At your size, I would say you need at least a large frame--you didn't say what size the pre-owned P2 is. If it is truly in new condition, the price seems reasonable since that bike retailed for around $900-$1000 new. I would always make a lower offer on anything used and see if you can negotiate some savings from the asking price.
Dave
EDIT: As this is a bike that may have been used for some extreme riding, query the previous owner about this and check the frame over very well for bent tubes and cracked welds--also check the fork and wheel true. The fork should move through the full range of travel without any clunking at either end.
That said, it is pretty important that the bike fits you and serves the riding style you are interested in. If you are interested in some XC or All Mountain, perhaps an AM bike might be a worthy consideration. For XC, the P2 might be heavier than XC hardtails. At your size, I would say you need at least a large frame--you didn't say what size the pre-owned P2 is. If it is truly in new condition, the price seems reasonable since that bike retailed for around $900-$1000 new. I would always make a lower offer on anything used and see if you can negotiate some savings from the asking price.
Dave
EDIT: As this is a bike that may have been used for some extreme riding, query the previous owner about this and check the frame over very well for bent tubes and cracked welds--also check the fork and wheel true. The fork should move through the full range of travel without any clunking at either end.