The warhead fired by the early Bazooka M1 of 1942 and M1A1 of 1943 had a lower armour penetration than did that of PIAT (3" as opposed to 4"). It wasn't until the advent of the M9 in October 1943 that the warhead became equivalent in effect to that of PIAT. Additionally the warheads fired by the M1 and M1A1, owing to their pointed shape, had a nasty habit of bouncing off the target at low impact angles; this was addressed on the M9 by having a much blunter shaped projectile.
The advantage of the bazooka was that the munition was rocket propelled so it had a slightly better DF range than PIAT (150yd as opposed to 115yd). However the bazooka had a noticeable backblast which would immediately give away the firer's position. Additionally said backblast made the weapon almost useless for FIBUA.
Bazookas were supplied to UK troops under the lend-lease program.