Thx for the tip, I'll open it and check labels on board.

I gave up. I've opened it and checked the numbers on PCB and they are exactly the same as you posted (HW:2521A MSB2521 GPS REV2.1).
So I've tried with Navon N490 firmware which was as close as I got regarding available firmwares but my device does not react with it. It seems that it's totally bricked or it really needs specific ROM which is obviously very hard to find.