What is Reddit's opinion of UST Reusable Hand Warmer?

From 3.5 billion Reddit comments

There's reusable handwarmers you could incorporate as well. Disposable ones would work but that might get excessive depending how often they're necessary. Apparently they regenerate with boiling water. get 2 and use 1 on each part of your commute (if that's what you're doing).

Note: I've never used them so I'm just trusting what the internet tells me.

Edit: There's all kinds, even USB rechargeable ones. That might be handy for hummingbird feeders in cold snaps.

You and a hand warmer in a reflective bivvy bag, in a synthetic sleeping bag, under a cheap down quilt. You can probably put it together for near or under $100 (these links total $114.66), and you have options to adjust how warm you need it to be, so it works winter and summer.

I used this setup (with a different synthetic bag that was on sale at the time) for some very cold nights. The heat reflective bivvy is a little uncomfortable sometimes, but it makes things so much warmer (and it’s much more comfortable than a Mylar space blanket). I now have better down quilts and no sleeping bag at all. Synthetic bags often provide better insulation, but are also bulkier and heavier than down. I needed smaller, lighter insulation. I also now use a USB hand warmer instead. Never tried hot water in a Nalgene bottle. ����‍♂️

This setup’s warm enough that I didn’t need to wear a lot of layers, just my base layer, wools socks, and a down jacket.