i have three petersons: a bent killarney, a system standard, and a sherlock holmes deerstalker. they all have p-lips and i really have no preference. for me, the system standard and the deerstalker are hard to clench because the stems are thick and almost rounded, though I don't have that problem with the killarney (the killarney does clog very easily though, whether clean or dirty, just from packing). of course, that could also be because the bowls on the system and the deerstalker are very large and heavy, so my jaw gets tired when i clench them (that's what she said--agggh! couldn't resist!). when i sit and hold my p-lips, i have noticed i have the unconscious tendency to sort of angle them upward so that the hole in the p-lip is more in line with my tongue.
i don't get tongue bite very easily because i like to smoke my tobaccos pretty moist. i never leave a tin open. in my experience, nothing is worse for a tongue bite than a cheap burley/virginia blend, and a p-lip might mitigate that somewhat, but i left those behind looong ago. as much like the fumes of hell good english blends can be, they never bite, unless maybe you try to smoke them through a length of pvc pipe or something, so i imagine the p-lip wouldn't make much of a difference with englishes.