You have to weigh up the likely hood of the flaps falling into the engine against any potential damage caused by removing them. I have not read on any of the Forums that removing the flaps has any negative effects, and in the short term this is true. Although what no one knows or seems to care about and I include tunners, indies etc. is the long term potential damage to the DPF.
I'll explain, swirl flaps are fitted to create swirl in the combustion chamber
swirl has a dramatic effect on reducing engine out soot or particulate matter or to most of us smoke. The very stuff the DPF stores and then burns off when it regenerates. So if you remove the swirl flaps the engine out levels off soot go up. Depending on the base engine and the calibration used, it can go up a lot. Remove the flaps and the DPF is suddenly getting filled every 100km instead of every 400km, so where BMW claim a DPF life of 100k miles, it has now decreased to 25K.
Plus frequent DPF regeneration increases fuel consumption and also the chance of fuel (used in post injections) entering the engine oil, leading to engine run-away and failure.
So before you whip out the flaps, just think about the above.
The only people who truely understand the use of swirl are the engineers who work for the vehicle manufacturer
that is what I tell my boss when I need a pay rise