Hi, I have one and really like it (despite just posting that I want a smaller, lighter double!). I traded in an older Sport to get it and even though the improvements aren't huge they are very useful.
Good points -
firstly the obvious, being able to use it as a single when toddler no longer needs it. But also, I've had a tired 4 year old in mine with ease (even in the second seat) so will definitely last you.
I like that you can put the bigger child in the back or the front (with the sport the heavier child always had to go in the front) so that if baby needs to recline they can go in the front and bigger child can sit up in the back.
I like the parent facing option - BUT you can use this seat with some of the older, cheaper P&Ts (not widely advertised! Probably to make parents buy the newer version)
I like that the seat fabric zips on and off - if you've ever taken a screwdriver to your older Phil and Ted to wash the seats after a baby has been sick in there you'll appreciate this point!!
It's very easy to push even with two toddlers in.
Bad points:
The hood for the second seat is rubbish. I've taken it off before now because it flaps about and annoys the child in the back. I think you can buy a spare front seat hood though, which clips on to the back.
As the second seat is quite far forward it doesn't leave much space underneath for shopping or nappy bags (you can buy pannier bags to hang on the sides but they make it wider - I tend to clip a child's ruck sack on the side instead). This does make it shorter than a lot of other tandems though, in fact it doesn't feel any longer than some of my single buggies.
The recline for the front seat is much trickier than it needs to be. The second seat has a little clip handle which is a doddle, but the front has straps and Velcro. Might just need practise to get the hang of as I've not really used mine in recline.
I've heard lots about the few weeks when a baby outgrows lie flat but isn't ready for sitting up yet but didn't really struggle with this. If you have the parent facing seat the baby can go in that with older child in the second seat (I think P&T said you can't do this, but you can!) or if its just a short journey you can pop a car seat on.
I hope that helps. Sorry I don't know the width but I've never found a doorway it doesn't get through - it even goes through my Lindam stair gate!