Wont work. Hardware of the Mio C520 is outdated and to slow to run Igo Primo. For me it was already hard to get iGo8 running on it. And 5 years ago it crashed with updated maps.

But if you want to unlock, go ahead. Here is the SD unlock:
[Only registered and activated users can see links. ]

Unzip and place in the root of your SD-card. Switch off the C520, switch on and wait for a few seconds. A script will be running and your device is unlocked. But trust me. You can better install Primo on your smartphone. I unlocked lots of Mio's like the C320, C520, H610 etc. But after iGo8 and Amigo the Mio's were outdated.