I just dont think the risk to the engine is worth it for 5hp.
Quite a few folk have noticed compressor tip damage when using aftermarket filters. Very fine nicks on the tips of the turbo compressor due to small particles of dust/sand etc hitting the compressor when its doing 100000rpm. I'm sure someone over on SRS put a photo up of the damage to his compressor on a 6 month old pair of K04's which he'd run with an open cone filter, and i too noticed damage to the compressor of the Scroll hybrid i baught used for my own car. So thats one example of an issue caused by poor filtration.
It also causes bore wear and valve seat wear as you would expect from flowing fine abrasives thru your engine day in day out for years.
You might think particles of sand are never going to make it into the inlet, But theres always dust/dirt floating around, especially on warm dry days, as anyone whos driven their car on a warm summers day will notice the thin film of dust on the paintwork after a drive.
Theres a reason that even high performance production cars where every possible horsepower is being squeezed out of them, still run paper filters. They quite simply are the only filter that will give your engine a properly cleaned supply of air.
I dont dispute that some of these products will give your engine more power, but so would running without any filter at all. Similarly inflating your tyres to 90psi or cutting off all the cars bodywork will make it accellerate quicker, but most folk are sensible enough to realise thats a stupid idea.