i would advise making sure your PA has a minimum of 31 keys. the compact PAs with 24 keys are simply not enough for itm and will drive you mad. ideal would be, 34 to 37, but there are compact PAs here and there with 30 or 31, which will suffice for itm....
when PA is derided as not suitable for ITM, i find that without knowing it, the critics are really reacting against the fact that many better-known irish/celtic PA players:
play hopped-up hyper-speeds
play hopped-up, noisy, untraditional-sounding ornaments
play (overplay) their PA basses & bass chords in a way that does not sound like itm basswork
play fusion-y arrangements including non-traditional-sounding backing and rhythm,
etc.....
these players are absolutely fantastic musicians and more power to them. but they do not sound like they are playing itm, and this is sometimes unfairly ascribed to inherent properties of the PA itself. true, the PA won't sound like the diatonic push/pull phrasing derived from the one-row melodeon and evident in the c#/d (or b/c boxes when playing flat on the "c" row). but pa's CAN phrase very traditionally in the vein of traditional fiddle or flute phrasing....
to my ear, mirella murray, alan kelly, and jimmy keane, who can all do hopped-up fusion-y stuff when they are in the mood, are simply gorgeous players of straight itm when they are playing more "pure drop" ornamentation and arrangements....i'm a particular fan of mirella murray, and alan kelly's cd with his brother john on flute, "fourmilehouse," is gorgeous traditional playing (different from his "Mosaic" cds, which are more world/fusiony-influenced).....here's a nice short PA clip from youtube, in this case an unnamed player:
http://www.youtube.com/watch?v=KpRFgBw-b9othe pa sound i don't care for is at the extreme opposite end of the spectrum from the super-wet scottish musette described above....i'm not a big fan of the bone-dry single-reed sound in either a PA or a diatonic. it is too antiseptic and denatured for me. but a "dry" sound with two middle reeds set at about 5/6 cents to be full and round, is lovely in both a PA or a diatonic....