The Thermacell makes the bugs leave not just quit biting but leave. I'm a believer, no experience with the pyrethroids but seems they need to get on you to get a dose, not so with the cell.
If you cover up exposed surfaces for biting insects, and most of us in the south and southeast MUST cover up, then KILLING the biting insects that make contact with us instead of just "shooing them away" makes this afternoon's hunt and tomorrow's and the day after that significantly less annoying.
Thermacell uses a synthetic pyrethroid that drives bugs away. Permethrin (ingredient of Permanone) is a synthetic pyrethroid that KILLS biting insects.
Do the math is all I suggest.
Thermacell heaters cost $30.00 (incl. shipping), an optional carrying case for $20.00, ultimately require rechargable "cigarette lighter" type butane supply (about $9.00/ea), and require non-rechargable pyrethroid-laced "patches" (about $4.00/ea) that are heated by the butane. So, to get started with a Thermacell expect to pay about $40.00 with follow-on purchases up to $20.00 per season (depending on use) to keep it working.
Permethrin (2.50%) laced insecticide costs $13.89 plus tax at Home Depot for 32 ozs. (one quart) that can be cut with water to make 160 ozs. (1.25 gallons) of 0.50% solution. This solution should last all hunting season depending on your individual use.
For the Record...I just bought my first Thermacell for duck hunting this season. I'll let you know what I think of it after the first/second/third uses.
It isn't always about the money. But it is worth the time to compare alternatives.