Melafix and Bettafix (just a diluted form of Melafix) contain melaleuca (tea tree oil), which can indeed interfere with the labyrinth organ. Some folks have had good luck with it, some folks have had bad luck with it. If you do use it, correct dosage is extremely important.
Pimafix contains, among other things, clove oil. Clove oil is used to humanely euthanize bettas, so you can bet that correct dosage is super important with Pimafix, also.
Warmth, aquarium salt, and maybe a little Stress Coat+ is a conservative approach that often gets good results.