I've been using them for going on 3 years with hundreds of hours wearing them and highly recommend them. I use them with the foam tips that come with them. ( Etymotic Research ER38-14F available on Amazon appear to be identical replacements ). I'm not sure if 40db NRR is right, but they're right up there with 33db non-electronic foam plugs. Some people use Peltor SkullScrews with them but at least in my ears the NRR seemed to drop significantly with those so went right back to the foamies.
I regularly use these by themselves at a 16 lane indoor range with mixed use rifle and pistol lanes. I have also shot comped handguns inside enclosed vehicles with only these inserted during vcqb type training. As long as you know how to properly insert foam plugs in far enough, these will stay put through most activities. I've done repeated breakfalls onto hard ground as well as ground positional movement with them in and they stayed put. As for comfort, I have worn them for 10 hours straight in training without any noticeable discomfort. The batteries started to go around hour 8 though without a break to recharge.
Make sure to buy from an authorized dealer if you do. Otto has been fantasic on the customer service front but I have had them replaced twice under warranty. The first time was after that mentioned long training day a few months after getting them, and when I found out one discharged a bit faster than the other. The second time was recently when one ear stopped charging entirely. In both cases I received brand new sets for no charge and quickly with no hassle. These plugs get a good workout with me and Otto has happily taken care of me each time. They honestly have some of the best customer service I have experienced anywhere.
If it helps, I got mine from
https://www.hitechwireless.com/coupon-codes/Around $410 now it looks like with coupon code.