I use adjustables and pliers wrenches quite a bit, but I almost never use either for turning bolts unless I'm using one as a "backer wrench" to prevent a nut or bolt head from spinning while I turn the other end of the fastener with a wrench or socket. In general, I don't find either one to be very useful for working on cars, so that might be why many here don't understand the hype.
That being said, they are both very useful tools to me. For fasteners or plumbing fittings over about 1" in size, I almost always grab an adjustable wrench, for fasteners or fittings under an 1" in diameter I usually grab a pliers wrench. In general, any fitting prone to compression deformation gets an adjustable wrench and any fastener with corners that can easily round off (like a thick plastic hex fitting) gets a pliers wrench. Small press tasks get a pliers wrench, metal bending tasks get an adjustable wrench or a pliers wrench depending on the scenario. Sometimes I even use an adjustable wrench to break a fitting loose and then I switch to a pliers wrench for quick turning of the loosened fastener. Pliers wrenches are also handy just to hold things sometimes.
In regards to pliers wrenches working with single-handle pressure, I say no. I have multiple 5", 7", 10", and 12" pliers wrenches (at least one old style and one new style for each size mentioned) that I have been using quite regularly for multiple years now. They have nothing close to the self-locking geometry and single-handle pressure grip reliability of a Knipex Cobra plier.
Personal testing- I couldn't get my 12" old or new pliers wrenches to grab anything with one-handle only pressure. My 10" pliers wrenches grabbed a few things, but there was often a little jaw spread before the mechanism initially grabbed, which increased the chance of rounding out the corners of the fastener compared to performing the same task with both handles being squeezed. For multiple scenarios I tried, my 10" pliers wrenches would also suddenly spread and let go after moderate torque levels were reached. Not the sort of scenario anyone wants to experience if you work in tight areas and value your hands. My 5" and 7" pliers wrenches grabbed quite a few things pretty well with single-handle only pressure, but that doesn't matter much to me because I personally use my 5" and 7" pliers wrenches mainly for holding and/or pinching small parts which always requires squeezing both handles.