I believe the issues that you have mentioned are probably a little over blown at this point and possibly caused by bad installations.I've been wanting to get them for a while but I've read a whole lot on them vibrating and issues with em. Put washers or somthing behind so they don't resonate and buzz, don't overtighten or they will break, and some just showing up to the door bad. I've been hesitant to replace 8 30yo tweeters that work just to have problems with the new ones over the next couple years. Do you think they might have all the issues they seem to have figured out by now?
I will say that I would not worry about having tweeters show up dead on arrival. It's been mine and many others experience that Polk has great customer service. When i ordered the replacements for my 1.2tls, two of the tweeters showed up with the terminals on the back side just dangling there. This was most likely due to shipping. I called Polk and they sent me out two replacements right away and wouldn't even take the others back. So i now have two spares that are fixable for free thanks to their customer service.