I have used several of these-


Plusses
reusable
cheap


minuses
EASY TO BREAK- I try to be careful, but the plastic does not seem to last all that long- most of mine broke/leaked within a month.

Short they only release heat for 30-45 minutes. Enough to shovel, but not that long

storage They do not STAY liquid; whether mine just get bumped in storage, or they somehow age; I I left it and came back a few months later, they were all crystallized, and had to be heated to use-

Bad QC- when I bought them, I would buy 3 or 4 at a time- they never maintained temp the same between each batch-