Hey Doug! Having grown up here in the oven region of our country I can tell you I have tried all of the mentioned products.
First, the cooling vest,
View attachment 203576
It’s filled with some sort of crystals that absorb water, you soak it in a sink or bucket, they swell up and then slowly release that moisture over the course of several hours on a hot day, there by cooling you down like a wearable evaporative cooler. Or at least that’s what the sales pitch is. I bought this to try and make it bearable to commute in the summer months here. I wore it under a mesh jacket. The reality for me was it just felt soggy and humid, it soaked the clothes I was wearing underneath and the worse part was water had a habit of draining to the lowest point of the vest then dribbling out. By the time I got to work my crotch was soaked and it looked like I peed my pants. It was a fail for me, I threw it away. Note: my vest did not have those ice pack inserts that the vest you linked to had.
Next up , the cooling neckband,
View attachment 203577
Made the same as the vest, these were all the rage here in Phoenix back in the 90’s, they were sold everywhere.
I tried one when I was a mail man during the summer months. I didn’t like it any more than the vest.
And finally something that I really like, the moisture wicking shirts
View attachment 203578
I have a bunch of these, I can buy them much cheaper than what Fieldsheer is selling them for at Walmart. They are 100% synthetic, mostly recycled water bottles. They do not absorb sweat, but rather wicks the sweat away from your body so it evaporates fast. I wear them when I’m riding , under my mesh jacket and I have found that to be the most comfortable combination. I also wear them on hot days when I’m out in my garage and when I’m doing yard work.
So there you go my