If anyone want to buy the OpenPilot GPS let me know, ill be starting an ebay page soon for all of you westerners outside of China who want a clone version of it.
No one actually tested those clones, how is the signal to noise under different conditions. Some cheap hardware can have noisy circuit thanks to cheap or improperly chosen capacitors or cheap antenna. Ublox has some guide lines on integrating their modules in designs. Each unit is usually calibrated to antenna. It's not as simple as putting similar components together and making it output something that looks like GPS coordinates.
Whats so great about DJI GPS in comparison to other GPS we normally use? ie NEO Blox 8M with built in compass (MAG)
Only OP GPSv9 is supported in current released version of Librepilot, as that is known to work.
I don't know what you are using "normally" but you must be talking about development code. As name suggest this code is not released. It's something flight-test team is trying.
The cheap GPS units from ebay with M8N are a bit gamble, they probably will be supported as PixHawk project uses them. I am lucky with mine, however people reported problems with noisy circuit or Mag dropping connection due to weak pull-ups (bad quality hardware). This is what can happen with every clone.
I agree with Alessio that DJI GPS is the way to go, if you don't want to risk money and get something that actually is known to work.