I don't really have much to compare to so I don't know how these compete against other brands. I got them because I like the black packaging and I needed to mail some things as I clear out my house to move. I prefer the plastic because it means that they are more waterproof than other mailers, but I have punctured at least one accidentally and without much force. I forget the circumstances under it, but the plastic stretched very thin and has a tear in it.
The adhesion doesn't seem bad, but because I had one bag that stretched thin like that, I use an extra piece of tape to make sure it's sealed, and package my items in an extra ziploc bag or bubblewrap to make sure it arrives--just in case there is a puncture or tear, I don't want water damage to get in.
I haven't had anyone complain that things have arrived damaged or that any of the bags have been maimed. Overall these bags have done well for me and they were reasonably priced, so I do think I will buy again, but it's worth being aware that there's a possibility that the bags may be punctured or stretch thin enough to tear. For $11 for $100 it was still worth it to me since I was still saving money despite choosing to package a little extra carefully.