I installed GFB DV+ on my M235i one week after HJS EU6 catted downpipe installation.
Very happy with it.
On-Off-On is now stellar. Throttle response was way better with HJS downpipe install and it's definitively sharper with DV+.
No CEL, no soft error, no odd motor behaviour.
Very nice product.
Concerning install, I removed stock DV only from underside of car. All I had to remove was the 3x water pump bolts on its holder.
Please take care that those water pump aluminum bolts must be replaced and correctly tightened (10Nm + 90° angle).
Cross thread about GFB DV+ on e90post for reference