Yes they work well enough. If we are both talking about the ones that come in a tin like for shoe polish.
Two of those will warm up a small delivery van,(personal testing) just remember to have at least one window open a little bit.
As with all gear, try it out before you really need it.
Just dont put it on the dashboard because you will make the windshield dirty and you might crack the glass from heating it too much in one spot (personal testing results). (In most cars the glove box door seems like a good spot to set it to me).
They are refillable too, all craft stores seem to carry beeswax and wicks.

Another thing that works are those little candle lanterns they sell to the backpackers. The flame is a little bit protected and they usually just go out if knocked over.