ive got the P3 and I never use it now, I bought a maclaren Quest when LO was about 6 months as the Pliko was just to heavy to get in and out the car and a pain to get up. HOWEVER if your not getting it in and out the car its good, although a bit of a bugger to steer one handed say if it pouring and your trying to hold a brolly as well lol.
I loved it in Pram mode (like with the carrycot) in pushchair mode though I was alwyas a little funny. from about 4 months when DS wouldnt Lay in the pram anymore, he also would only sit in the pushchair for a short time before kicking off and crying to get out, in the maclaren he would sit in it for tripple the time, maybe it was a bit uncomfortable for him as he isnt to bad in it now. The only thing I didnt like was on mine its not like and attached harness that comes from the top over the shoulders attached to the back bit, its just like you hook it up arround the shoulders and its only attached round the waist meaning DS can learn right foward and over - its a bit strange. TBH I love the maclaren far better, but also think there are much better travel systems out there for same / cheaper money that do a pram and buggy mode!
Re the car seat there are pros and cons really - its very sturdy which is great and mine came with an isofix system so it was always easy to put in car - plus also fits without the isofix so if was going in someone elses car was not a problem but it is quite a heavy one. Once DS got to 6 months it started to be REALLY heavy to carry him in (before them it was just quite heavy lol) - it is supposed to last till they are 15 months but this is not really possible for a few reasons IMO a) he is 10 months no and I can barley carry the seat with him in (and Im not exactly a weakling!) b) his feet hang so far off the end, I have to have the front seat of my car rolled so far back so his legs are not squashed up c) his head is now level with the top of the head rest thing (its moved up to max position) and once it gets there you need a new seat so in the next month or so we will be getting a foward facing one. There is another pro and con to it - its quite an upright seat, this is a bit to upright for tiny babies, he always seems to scrunch down but from....oooo I dont know maybe 6-8 weeks he didnt seem so bad, but then again from about 6 months he looked and seemed comfortabler in this one than mum & dads maxi cosy as that was more laid back and he always wanted to sit up not lay so he used to kick up a bit of fussy going in theres. He grew out of the maxi cosy one quicker, they had to get forward facing last month. Maybe you could find a compramise car seat - inbetween the laid back maxi cosy and upright M&P lol. Check out the Britax First Class I think it is - think that is birth to 4 years so starts of rear then goes forward facing, plus is a best buy & which safety best or something. I wish I had seen this when I got my M&P travel system!
Anyway - hope I have helped, any questions, give us a shout!
To sum it up - although I 'liked' the thing didnt love it and wish I had shopped round more for a better one and a different car seat rather than jumping in with the M&P just because it was half price (Paid £240 for the lot) - I certainly wouldnt pay full price TBH
(ignore the dodgy spelling I cant be bothered spell checking lol)