InVade Bio Drain 1 Gallon (Original Version)

I have used drano gel is this a good product. I only have a few at a time is this normal put in new bathroom three years ago have them off and on.

How much do you need to use on each drain? (2 cups? The whole gallon?)

What's the difference between 'original' bio gel and ibdc128? i got the latter still have a few flies after 3 weeks, ready to buy which should i get?

What are the chemical ingredients?