I really really like the Ice Vibe boots. I actually really like the ice packs too. I don’t know what they fill it with, but it seems to get colder/stay frozen longer than your regular pack - though they are thin. I bought a backup set of ice packs, freeze them at home and then wrap one inside the other, and then wrap that in aluminum covered bubble wrap (can find at Home Depo, its some kind of floor insulation). They stay ICE cold even after a few hours.
I bought them for my driving horse who has a known shoulder/tendon issue. When we did some blocking, he seemed to have a pain point right around the fetlock. It was mild, hard to pinpoint, and the only recourse was injecting the tendon sheath. Vet suggested trying icing first, so hence the Ice Vibe boots.
They did seem to work on my horse, he enjoyed them and seemed comfortable in his work.
HOWEVER, anyone I know (humans) who has arthritic knees or ankles or wrists, LOVES them. My friends and family get way more use out of the IceVibes than my horses ever did. They all swear that the pulsing action really drives the cold down deep. I haven’t had a need to try them out myself, but my friends swear by them and ask to borrow them all the time.