I'd just look for what people say in the bad reviews. I generally use mine on the lowest temps, 80 or 90. I don't know what kind of maniac would use them at the higher temps. Every time I turn it on I have to press the button to cycle through the temperatures, a mild annoyance but NBD. It automatically turns off after a few hours which is a feature, not a bug. It used to be that I'd sit down at my desk and my hands would never warm up, now they warm up from the mat and stay warm even after the thing turns off.
That is a much bigger pad than what I've used! Wow. That's amazing.
I've used a oversized body wrap pad (120V input) and a 24V pad with wall-wart designed for mini-green-house seed planters. The former was comfortable & wrapped in soft, but wasn't a great mousing surface. I do want to point out: in my experience, these are nice for the arm, but notably the keyboard and mouse never really warmed up very much, both remained a bit chill, back when I was in a fairly un-warm draft-y room. It was still really nice to have, but my hands could remain kind of chill, I'd still keep on my nice fingerless gloves. Still, a great addition.
Some of the amazon ones are barely 6 months old and are failing at the 6 month mark. I picked one of those. Be weary of high review counts, and ensure the reviews are all for the particular product.
I'm guessing you want one with a low enough temp setting that it doesn't bake your keyboard. Around 80-90F degrees I'd guess, but haven't tested. Especially important if you have a 'smart' keyboard, which has an actual small computer (more than an i8048) in it.
I'd just look for what people say in the bad reviews. I generally use mine on the lowest temps, 80 or 90. I don't know what kind of maniac would use them at the higher temps. Every time I turn it on I have to press the button to cycle through the temperatures, a mild annoyance but NBD. It automatically turns off after a few hours which is a feature, not a bug. It used to be that I'd sit down at my desk and my hands would never warm up, now they warm up from the mat and stay warm even after the thing turns off.