testing your mod...
Phosphor is, IMO, of limited use: less range and less radius than regular smoke. Not so good for cover, but you have 4 shoot with very low time usage, so maybe is OK.
Nitrogen is good. It will be a valid alternative to stun rod on early game. It will become useless when small launcher is discovered but this how it's supposed to work. Like it.
Napalm is gold! 10 shots, limited weight. Better than any other fire weapons. But being a fire weapons is of limited use, just as intended.
Chem Waste: OP? Not much. This is why:
Limited range, no radius. Being the chem thrower a support weapon, you will carry a secondary weapon. But chem thrower is a 3x2 item. Waste ammos is a 2x2 item. You really have to carefully choose your equipment. Very wise choice tollworkout, hat off for you.
You have balanced the weapon not with stats alone, but using encumbrance too!
Maybe reducing ammo from 12 to 6-4 will resolve the OP problem (just a suggestion).
Toxy-suite: a very light armor, limited use. OK for an early armor, but why the alloy requirement? If I research alloy, the Personal Armor is a much better choice. So, please, remove alloy as requirement or make the toxy available to buy from the beginning.
I will throw you an idea: what about giving the toxy-suite a huge under-armor (only the under!) of 80-120? This will make the toxy a bomb squad-tipe armor, useful for stepping over mines. This way you can make the toxi-suite a bit more useful even when Personal Armor is available (personal opinion, do what you like).
Research: When I start a game I, like most players, want laser rifles (or heavy plasmas) as fast as I can, and I tend to skip non vital equipments. The research requirement for chem weapons are not so high but are lengthy... What if chem weapons will unlock something useful really quick: chem thrower + phosphor + napalm or chem thrower + phosphor + nitrogen or chem thrower + both, just with only one research (maybe make them costly to produce).
This way players will be less tempted to skip the research of chemical branch. Later in the game the chem weapons will lose effectiveness (exception for chem waste). You must have them very quickly or you will end not using them (with veteran soldiers and Flying Suite, fire, and smoke are less important).
This was my review. Trying to be useful, sorry for being over critic.
Your mod is a worthy addition to the battle against the alien menace
Keep on with it, and thank for sharing.