I've got one, what do you want to know??
I loved my old GTI, but I'm no badge whore - I've had most makes and buy on merit, rather than loyalty. As good as my old GTI was with all the work I put into it, the 135i is a better car in every respect straight out of the box, other than practicality. It seats 4
just and the boot whilst big in volume, is tight in terms of the small letterbox opening you have.
I get 340 miles to 50lts commuting. Not much different to my st2+ DSG GTI to be fair. It rinses through fuel when giving it some, but what 6-pot, twin turbo car doesn't?
Similar power-weight ratio of my old Golf, however my old Golf had coils/ARBs/Alcons/WALK etc etc and despite all that, the 135i was quicker around Rockingham t'other week on nothing more than a set of decent tyres. The handling out of the box is astonishing, however they are appalling on runflats which most will be on - so don't let the test drive fool you.
You need confidence to get the best out of them, the Golf you grab by the scruff of the neck and you can drive it at 10/10ths immediately... the BMW you need to learn, and it rewards accordingly.
Quirks:
'box almost feels like it has straight cut gears and the race-type clutch has to be treated with a bit of care, don't rush it. Heel and toe very much required for fast downchanges, otherwise you'll swing the back out.
Long gearing (LSD sorts this with lower final drive) does 115 in 3rd!
Very linear, so N/A like delivery with flat torque. Can feel slow, really isn't.
215 front tyres too skinny. Apparently downsized to build in safety understeer, up them to 225 and it becomes more neutral again.
Common faults:
HPFP/coilpacks/injectors/valve lifters - all should have been sorted on recall/warranty.
Mods:
Power is obvious, a map alone giving c.370BHP. I'd do this last.
Brakes are already superb, lasted all day on track with no issues. Pads and Fluid are all that's required for serious action.
Handling lots of scope. Because it shares the E90 3-series running gear, pretty much all the M3 kit bolts straight on (which is what they've done with the 1M). Straight off the shelf from BMW, I got the following for around £550:
M3 wishbones. Spherical bearings, lighter, adds 1.5degrees neg camber in addition to knocking out the camber pin on the strut.
M3 ARBs and all associated bushes, clamps etc
I also got spherical bearings for the front tension struts and uprated rear subframe bushes. The steering feel now on the old-skool PAS quick 'rack is soooo nice, feedback is near Porsche like.
Now, aside from a few differences, my underpinnings (well, the important parts) are pretty much the same as the 1M. Only the track width can't be replicated.
An LSD is very expensive around £2k for a manual via the aftermarket like Quaife, the stumbling block swapping to the E90 M3 being the input shaft on the prop, but now the 1M has engineered its way around this, I expect conversions will start soon when people have looked into it fully.
It's a wonderful car, and the closest thing I've driven to an E30 back in the day.
