Ta da ! The hub is back !
OK. Here goes:
(1) Lovely woman running rubadubdub in Crouch End. Patient. Helpful. Had both Terrain and Urban in stock. Even the rare 'pink flower' design which looked gross in photos on the Web looked quite cute in RL.
(2) Tried both buggies, but only pushing them around her small shop - not outside. Open and folded both several times, did a few tours around the clothes rack, tried turning around on the spot, tilting up the front wheel to get over an imaginary curb etc. etc. I did NOT get a chance to try the Urban in swivel-locked mode because there was a bomb scare and the police ushered us out of the shop...
Anyway, conclusions:
Both are nicely made and, as Ms. yumyum stated, you'll be happier with either. They're both strong and simple. However, I'm going to be buying a fixed wheel Terrain. Here's why:
Pushing the two buggies around the shop, the Urban was easy peasy to turn around a corner, or cruise in a circle around the clothes rack, and with the Terrain you have to push down on the handle to lift the front.... BUT the Urban is more than two inches wider and we kept catching display items. It is 1 kilo heavier and the weight is more over the front steering wheels so lifting its nose for a curb will be more tricky. You feel a tiny bit more friction pushing it.
Because the Terrain's mass distribution is MUCH more over the rear axle, only a tiny push down on the handle bars and the front is lifted. It is a superbly balanced machine. I honestly do not think you will have difficulty in shops etc. particularly if you don't spend your life in little boutiques or exhibition halls all day, every day. The pedestrian dodging I concede might be more difficult in the Terrain, but they'll get out of your way, and you can spend your time simply pushing rather than pushing AND steering. You WON'T be stuck 'trying' to turn, and then feeling the weight. It is simply not an issue. Even if the child is older / heavier, the centre of gravity and weight distribution work in your favour.
When folded, you can really feel the weight difference picking it up as a deadweight. The Terrain is only 1 kilo lighter, but it's just light enough to feel 'nice' to pick up. The Urban (perhaps also becuase of its extra width) felt more cumbersome and heavier. I noticed a big difference and I am a big bear grappler.
BTW: both models are freestanding when folded ! Not super secure, but could be tucked behind a door etc. To make the Urban stand, however, you must fold the adjustable handle all the way in - annoying when the Terrain (with its fixed handle) needs nothing.
I cannot yet comment on the different types of seat available for the Terrain, but can advise that I've seen buggy bumper bars (with toys etc.) advertised on Web sites so I am sure we could find something that fits.
Pinkmama mentioned the brake, and you can only get that on the Terrain.
The Terrain is shorter (when erected), narrower, lighter, cheaper, stiffer, simpler. (A bit more 'stroller sized'). It has fantastic balance. It is the one for you and I, shweetie, esp. if you do a daily doggy walk and are contemplating a move further out into the country.
I now would not hesitate to buy a Terrain.
The hub has spoken.