Got a Phantom 4 pro and fancy a Spark for the portability. Keep reading these posts about flyaways, compass errors etc, something I've never had since I had a vision plus. Has anyone any idea what percentage of Sparks are absolutely fine
I really can't  be doing with compass errors etc

I would do a parallel between SPARK and any new iPhone release for example. Having that in mind , I would say the % of complains here , by the number of users on this forum, and by the number of units they may have sold, is pretty low. Having that aside, the issue with SPARK "fly away" or just dropping from sky is pretty concern. I think the DJI QA department did a pretty lazy work in not capturing these major concerns in advance. In theory we can't fly a drone in a area busy with people, so I didn't see any lawsuit so far, what can easily happen if a drone drop on someone.

According to dji admin we are just biased users

I understand the concern. The Spark is a very reliable aircraft with much of the latest technology and anti crash software. It is a superior aircraft to the Phantom 2 Vision Plus.

Compass problems are usually caused by RC pilots, not defective products,