Agreed - it works well enough on the Scottish midges, though maybe the Mexicans are tougher ?!
A-SSS - Don't do a thing for No-see-ums (Canukistani midges) 'cept maybe as salad-dressing for the little bastards to enjoy whilst dining upon your flesh.
If it all worried when you are out in the bush, like I said above, do the military thing.
Permethrin treated clothing.
Deet on exposed skin.
Nice thing about Permethrin treatment, it does not wash out easily as it binds to the fabric, and will last and remain effective through a dozen or so washes. The treated clothing is available commercially, but it is usually more cost effective to put together a clothing set of shorts, t-shirt, ls shirt, sox, hat, bandanna and long pants and shoes and treat them yourself. Don't forget things like backpacks or guide bags you may be carrying. Do not use on your skin, it is for clothes and gear only. It will irritate your skin, and also not bind properly and provide little if any protection.
Permethrin can be purchased through animal husbandry shops in 10% strength. Commercial clothes treatments are sold for more money at 0.5% strength. Buy the 10% and mix it down to 0.5-0.75%
Take freshly laundered dry clothes and spray them until they are thoroughly saturated, or preferably put them in a pail of solution and saturate, wring just enough to prevent dripping, then hang to dry. Treatment and drying should be down outside.
Keep any remaining solution bottled, labeled and secure. This is NASTY stuff in unbound liquid form and will seriously mess up water waterways. As well it is neurotoxic to insects and will kill bees so don't spray around the garden. If memory serves it is also toxic to cats. So, in other words, do not pour leftovers down the drain, but dispose of at the hazardous chemical depot.
When dry on clothes it provides no issues if you need to cross streams or other waterways.
With regard to DEET - Minimize exposure time if possible, so wash off when back indoors.
I have spent 2 weeks at a time covered almost head to toe in 100% Deet whilst on canoe camping trips many many times over the years. It is can be nasty stuff with regards to some (not all) plastics, but is very effective at what it says on the tin. Just have to wash your hands directly after application.
Also, if using a liquid, non 100% Deet, look for one that is water based such as Ben's. Much nicer on the skin etc than the oil based.
Thermacel do work pretty good in a calm setting for a small area. Being they use a butane cartridge to heat a vapour pad, they are susceptible to windy conditions, but are an effective secondary method to reduce local populations, such as on the patio or under the kitchen / dining tarp out in the bush. They are not a substitute for proper clothing and sprays and lotions. ...and in an enclosed location - Nope - inhaling poison is not good, well ventilated conditions only.
Have spent many weeks combined in Canada, CostaRica, Mexico and Cuba without issue and very very few overall bites. ( I also have bug-nets for when it gets bad in Canukistan, but have never had it bad enough for use out of country.)
YMMV
Good Luck and enjoy.