The P-1 was one of the first guns to use an aluminum alloy frame. I agree they are a smooth firing gun, excellent to handle. But be advised - do not be tempted to shoot hi-power ammunition out of it, even if and especially if, you're tempted to try hi-power ammo after installing extra strength recoil springs. Simply put the frames can crack, even a 1979 issue with all the various improvements and part upgrades incorporated into the design over the years. You can shoot el-cheapo Wal-Mart Winchester White Box bulk ammo all day long. The P-1 is a fun plinker, a classic design, and an inexpensive piece of history, but stick to the ammo loads it was designed to shoot or expect to keep it as a paperweight.
This advice comes from both numerous reports and personal experience. I bought a P-1 that was on consignment sale - the previous owner had used high power ammo and tho I never did, I discovered a small crack in the frame about 6 months after purchase.
FYI a great site for all things related to P-1, P-38 and other Walthers and German guns is.