it is possible to have too much heat so I caution against using hand warmers on top of toes, against the skin, or over thin sock liners. the hand warmers are best over the top of thick socks

there are different types, meaning some last 4 hrs & some last longer

there's also a new type of toe warmer, I think it's called super toe warmer, so they are larger & last longer

I have been disappointed with/ some toe warmers that stopped heating before I needed them to. it's always a judgement call which type to use for which activity depending on conditions. meaning on one end of the scale, if it's not very cold & I won't be out more than an hour then toe warmers are fine. at the other end of the scale, if I'll be out for 3 hours snow shoveling & roof raking w/ uninsulated rubber boots, then definitely hand warmers

a bit of trial & error will give you a sense of what works for you, in various conditions

yesterday, 30 degrees, had to do my winter wheel swap on my car. expected to be out there for an hour or so, 1 pair socks & toe warmers was perfect