I frequently get questions regarding aftermarket MAF sensors/descreening and what gains they will net. My answer to that question 9 times out of 10 is: NONE as the OEM unit can handle ~550HP.
The aftermarket MAFs are not calibrated the same as the stock MAF. So, for a given volume of air, the aftermarket MAF will underreport that volume, this causes the PCM to increase ignition timing slightly, which is the resulting increase in power.
When tuning for an aftermarket MAF, the PCM will be recalibrated so that the MAF reports correctly (or close to correctly), thus leaving no real benefit to the aftermarket MAF. Descreening has the same effect as an aftermarket, and has no benefit other than underreporting the incoming air.