yea a pm5 is a proto matrix 2005
the only thing with buying new is u have to use it for a while and keep an eye out during maintenance before it will shoot as well as a broken in gun.
imho u have a paintball shop close by dont u??
if so there should be no problem if you buy second hand because even if they deal in other types of guns they may be able to point you in the right direction of someone who knows what they are doing.
if you think you are going to have problems then buy new
otherwise you may aswell buy second hand and use the saved money for other equipment or training