Hi there,
I've recently bought F30 without M package because I found a great offer of the car(low mileage, 1owner, car on warranty etc) and Im planning to add m stuff same as you
I've been looking for rear and front bumpers however in country where I live there are not much bumpers in good condition so I've read through about those not OEM bumpers and they seem very reliable. I am going to buy similar package as you - you can always try to fit them before painting and if it wont fit perfectly I believe you can get a refund or at least get another bumper that will fit
So Like I said i've read a lot about them and asked people from polish Bimmer forum and most of them said that they work just fine
Good luck