Didn't myself and it's been fine.

The DP one shouldn't as it's a Ducati part, and unless the Staintune one is proved to be the cause of a problem I can't see that being an issue either IMHO.

Hi Steve, I'm the organiser for the Sussex area and Roy usually brings a group over on the 3rd Sunday of each month, look forward to seeing you there.

I had the DP cat bypass fitted to my 1000DS with the DP air filter. Does improve the sound but not to open pipe levels. One of our kin had termi end pipes as well as the cat bypass and it was probably just a bit TOO loud at times, you'll find that excess noise is almost as good at attracting attention as small plates. If you go the DP route you won't need extra dyno time, just spend a bit of time getting used to it and dialling the suspension in for your preferences, it's really bouncy to start with and takes a long time to bed in.
Have fun mate, welcome to the fold.
Caffe latte por favore!