I bought the Phil & Teds sport buggy when I was expecting my 2nd child with an age gap of 17 months. My eldest only started to walk at 15 and a half months so a double was a real necessity especially as I don't drive and walk a lot. I found it made life so much easier to be able to put them both into the buggy and just go, so definitely would recommend this as opposed to the suggestion of a single buggy + sling, or single and get the toddler to walk, for mums in a similar situation to myself.
Compared to other doubles I felt this is the best option for getting on the bus and into narrow doorways or shop aisles. It is wider than most singles but only slightly, and is much narrow than a side by side, and also much less cumbersome than the one in front of the other type double buggies which take up a lot more room on the bus. It is ever so slightly to wide to go through the gap between the pole and the seats on most London buses so unfortunately do still have to ask the driver to get on from the back door most of the time.
The main critisism I have heard from others about the Phil & Teds is that the 2nd child is too close to the floor and low down, but my children never had a problem with it. My older boy used to go in the back seat so that he could hop in and out when he wanted to walk or sit, and now my 3rd baby is in the back and he seems quite happy and content there. I never had a problem with them being unhappy with the 2nd seat.
I am now using the pushchair for my 2nd and 3rd child as I had the same age gap again, and the pushchair is still going strong although a few signs of wear and tear but still functioning absolutely fine.
The downside I have had is that I have had a few punctures on the wheels, so would recommend getting a spare wheel to keep for emergencies. It is quite easy to take the wheel off and put a new one on, so if you have a spare then this is not much of a problem as you can get the other one fixed in most local bike shops. It is worth this slight problem to have the pneumatic tyres as this makes the buggy so much more comfortable to push and also really easy to bump up and down steps. I take it regularly on the tube so that is invaluable to me as you would not be able to pick it up and carry downstairs with 2 children inside but I can easily bump it up and down without any help, due to the strength of the tyres.
It is a very hard wearing buggy and stood the test of time for me, as it has been heavily used for over 2 years now and still going strong.
I do find it quite hard to fold down but for me thats not too much of an issue as I have no need to fold it regularly.
Overall I would recommend it for any mum with a small age gap, especially those who walk a lot.