Liz ~
I'm not sure how helpful my experience is because I underwent the 'retro' surgical procedure and don't have a BAHA. But, for what it's worth, I have the titanium mesh and I've never experienced any problems because of it. None. It's use is fairly common with AN surgery and I doubt it would still be used if it posed a serious statistical risk to patients. Doctors could be sued for willful negligence if they were using the titanium mesh and it was known to cause serious problems for patients.
Unfortunately, as with most medical issues, one size does not fit all and for the unfortunate few, such as our friend, Mei Mei, the statistics don't mean much when you're the person who pulls the short straw, as it were, and have to deal with pain, suffering and numerous medical procedures in an attempt to rectify a situation (the titanium mesh) that you had no control over.
I would suggest that what it comes down to is taking a small but very real risk that the use of the titanium mesh will pose problems for you, post-op. I believe that the skill and knowledge of the doctor performing the surgery is a major factor in securing a good outcome to AN surgery, with few or no complications. Because many AN surgical patients have had the BAHA implant over titanium mesh with no real problems (e.g. Jan B.), I believe the risk is relatively small. In addition, your HEI doctor seems to take very reasonable precautions with the mesh so on balance, I don't see any reason to fear it.
Because AN surgery is invasive and complicated and thus, daunting for the patient, we can drive ourselves crazy playing 'what if?' Since we cannot know the future, we simply have to take some risk while doing whatever we can to minimize the chances of post-op problems. Being informed is critical but using information that (inevitably) suggests possible risks, albeit small risks, can be counter productive and if we added up all the 'what ifs', few AN patients would ever agree to undergo surgery. Of course, then we have the risks that come with radiation, so there simply is no panacea. We do what we can to keep the risk of potential post-op problems small and much of that is linked to choosing a doctor/team with extensive AN surgical and/or radiation experience, as you have with Dr. Slattery at the famed HEI. I know that you trust the HEI doctors and I'm confident that your trust will be rewarded with a good surgical outcome.
Jim