I have been a user since day one after purchasing my PiPo M9pro wifi only (but able to support 3G dongles with latest at end of JB updates firmwares).You can imagine the hectic flash/reflash from August 2013 to date it was at least 1 updates a month since 2013 and I have never faced the issue of "flickering screen" whatever you are facing seems, I suspect is more of a hardware issue rather than software one.

But that is my opinion only , since I am not holding the device in my hand and able to inspect it closer, I would check the display connectors, the display IC, and power connectors to the screeen/backlight, since any body who has opened up ANY tab/device (especially me) will vouch that after opening it and disturbing ANY connectors would result in other non related problems cropping up, like another broken connector/wires while doing the the "repair" inspection. I have a few pads at home without spare parts after trying to "inspect" repair works. Mostly connectors.

I presume you are using another Customs ROMs from another similar site (supporting heavily on M9Pro?) Kasty's version is as close to the factory ROM as is possibly possible (except init.d enabled, bigger data partition for this version 7GB, no PiPO apps/launchers)Never heard of "flickering issue by users of KASTY ROM ecept lastly they found out that it was a hardware issue.

So switch over to KASTY (I was a user of the other ROM too before, until I encountered a lot of issues with it since they try to mod it heavily)