I have one as a company car.
Economy ranges from ~34MPG average to ~40MPG (cold/warm weather).
The thing takes off a bit over 5K RPM, but it's never very quick. Handling is brilliant TBH. The car feels quite tall, but it hides it very well indeed and it corners like a go kart. Steering feel is excellent and very precise (better than my CTR by a long way), and the gearbox is pretty good and has a nice short throw (not so good as my CTR). The traction control is never very intrusive, i.e. I've only really had it kick in when flooring it out of junctions in damp conditions and when going sideways on roundabouts. Oddly, it does tend to snap oversteer when on the power (and you're being very stupid) and will drift a little if you really, really push it. Seats are okay, but a little narrow so the bolsters dig in my thighs very slightly (I'm 6'3" and not particularly fat!). The driving position is very good, but I have to have the seat right back and as lows as it can go. The foot controls are very, very light, and I find the car very easy to stall due to their being zero feel to the clutch. The brakes are a bit off/on as well.
It's quite a bit roomier than the Cooper, and the boot has a false floor that you can put shopping under, so it effectively doubles the boot floor space. You'll reasonably comfortably fit 3 passengers in the car, even with the odd tall person.
As for interior build quality, well it's crap really. The dash controls are flimsy but functional, and all the plastics are pretty dire. The fabrics are generally pretty cheap too. The stereo is pap, well at least the speakers are. Rattles are part of the package, so you'll have to live with them whether you like it or not. It's a very nice looking car as superminis go, just not brilliantly built.