Any intervention to any one individual is going to impart some risk, no matter what procedure or medication we're discussing. There are so many factors, not least of which is the overall health of the patient and the 'condition' of the person performing the functions....his/her state of mind, health, distractions, accidents in the laboratory/surgery/clinic,...

If we could assume that the patient's health is 'nominal', even with one or more comorbidities that are being managed well, the surgery is clean, no pathogens, and the surgery team is on top of their game (it's a Tuesday, Wednesday, or Thursday, and it's not an emergency where they all had to drive back to the surgery, gear up, gown up, etc), the risk from the implantation of a Watchman would be no greater than a mitral valve or aortic valve repair lasting about the same length of time, same anesthesia.

These are close to rocket science, but dated rocket science, and it is being done everywhere in the western world all the time, every day. These are pros who work in clean labs, know how to keep their patients safe, how to help them recover, and so on. It's routine. So, the risk to placing a Watchman is low. Even a colonoscopy has some risk. Maybe that will help to situate it for you.