I have but it's very costly. 950 pounds just for the parts which consist of new fan assembly and various other bits.
It's about 1500 all in. DTUK piggy back chip is 399. A little more crude but quite advanced now compared to a few years ago.
I'd be looking at 219bhp so a good dollop over the 181bhp standard.
The only reason I'm considering this is because I drive rather a lot on fast A roads from South Wales to North Wales up through the Brecon beacons on the A470 to my parents in the Porthmadog area and overtaking in the 520d is a sphincter twitching experience at times in standard guise. Great in the C4S, simply one of the best 3 hours you could spend behind the wheel anywhere. Just looking to make driving up there with he BM a little more safe an effortless.
I'm going to run the car in before adding anything obviously, prob do about 2000 miles then add a chip. I'll let you all know how it performs. Would be interesting to hear of anyone else's experiences in the meantime though.
Info here http://www.diesel-performance.co.uk/bmw-diesel-tuning.html
F11 520D M Sport (Power Kit)