To further confuse things, I'd like to add that I find all three of my P-lip bearing pipes to be different. I have a 303, which has a small, very thick and round stem, a much older 606 with a saddle type stem, and the 140th Anni. pipe.
The 606 is really comfy... I love it.
The 140th is tolerable, but I made a fishtail replacement for it all the same.
The 303 is no good in the front teeth, but excellent for clenching.
I do find with all P-lip type bits that my throat becomes a bit irritated if I smoke a full bowl in one go.
All in all, I'll stick with fishtails when I can, but a p-lip won't stop me from buying a pipe if I really like it and can't get it with a fishtail.
i don't like the P-lips at all. i reshaped the ones i have into a modified fishtail. P&C sells fishtail system stems, but you'd probably have to send the pipe to Peterson or a repairman for any of the other models.