Trust me, they don't work. At least, not very well. I dive in colder waters (Vancouver Island Canada) and my hands get cold pretty quickly. My drygloves have no built-in liner, so I'm always trying various liners. I bought a pair of 2mm kayak neoprene gloves a couple of years ago and tried them. They were ... OK... in the summer, but as soon as the weather got cold they were not good at all.
Part of the problem is the neoprene will crush at depths over 60fsw and by 100fsw you lose most of the insulation they might have had.
I've since gone back to some lovely yellow "work liners" I found at Work Wearhouse locally. I have buckets of liners and these yellow ones seem about the best so far.
One other liner tip - wool works great until the glove leaks. Then the salt water will shrink and 'set' the shrink permanaently, even if you rinse the liner in cold water. After a leak, wool liners are pretty much garbage. Synthetics are the way to go or so I've found.