You used to be able to visit Heinnie's, but I'm not sure they still have their showroom, let alone whether it's going to be open in the current circumstances.
The way I do it is to buy on forums and sell on if I don't get on with it (that's not very common!), but I know some do take advantage of the very generous returns system of Heinnie's to do similar.
You'll be hard pressed to go wrong with a PM2 in G10, but the Military won me over so I flipped my PM2. The Para 3 I gather was not a success in G10, but has done extremely well when in FRN.
If it was between the PM2, PM3 and Manix 2, I'd be getting a Military