When I use Etex I use the flexcoat syringes and mix really well, and never have a problem.
Once I switched from weighing to syringes, I never had a bad batch again, and I can make up more quickly and accurately, if I need it.
I drilled a small hole in the top of each bottle of the Etex, and leave the syringes stuck upside down in their respective bottles. Their tips are slightly tapered, so a hole just larger than the tip will make a snug seat for the syringe.
When I want to mix, I hold the syringe and turn the bottle over, so I can fill the syringe without air getting trapped, like filling an insulin syringe. Once I have the amount I want, I turn the bottle back over and remove the syringe.
It is as close to idiot proof as any method I've ever used.
Etex is a decoupage epoxy, meaning it is designed to go over large wooden surfaces that can expand and contract, like bar and table tops, so it remains more flexible than glue epoxies like D2T, which are designed to be rigid.
Measuring by volume, not weighing, is the only sure way to get exactly the same volume of the two parts. I spoke to the Etex technician and that's what she said.
After I mix the snot out of it in a small solo cup, I hit the bottom of the cup with a hairdryer, so make the epoxy more runny and help the bubbles come up to the surface, where they are easier to break.
It is a great material, so I hope you figure out a method that works for you.