Not dangerous, and much safer to use than the leaky plastic primer carriers in the OEM breech plug.
Are you planning on shooting Blackhorn 209?
If you have any questions, I was the crash test dummy with that plug 4 years ago, before it was released. I have tested it extensively with Blackhorn 209 and around 11 or 12 different 209 primers, but it works well with any black powder or black powder substitute.