Assuming that these zipper chaps are well made (zippers hold up etc.), the 2 questions I have are:
(1) How easy are they really to put on /take off?
If they are a PIA, the advantage is lost. If they don't stay zipped, there is a problem.
(2) How do they fit?
The advantage of straps and flaps is that they can easily adjust to different diameter leg calves. Maybe the zippered ones can be looser because they have protection all the way around, so even if the chain spins them . . . ? Might be an individual fit thing.
. . . there is a huge selection of chaps for sale but a lot of them are 'rebranded' and come out of the same factories. Husky and stihl don't actaually make chaps but sell them . . .
I have seen a lot marked 'Made in Mexico' and 'Made in Canada' chaps here. I assume that a lot of the stuff for European markets are made elsewhere - different specs, EU requirements, import duties, etc. The UL rating is a good first step. Note that the Oregon chaps have different chain speed ratings, and some of the chaps describe different types, and number of layers, of protective fabric. I have not been able to find a uniform standard for how those chain speed ratings are determined, even after asking a few reps.
Philbert