I owned couple Toyota before. They are old and cheap, so I didn't
bother put in the Toyota coolant, just Pretone. I replace the water
pump at at 100K, so never know any effect.

I would use ONLY distilted water even for flushing and filling the
reservoir later. This is more important than what type of coolant you
use. Distilted water will ensure that there is no bad stuff that will
cause your system to rust, nor get hard deposit.

I think Zerek stuff is pretty decent, but do you want your car to be
the test vehicle? Since you are saving a lot of money by doing the
maintenance yourself, why not spending a few more bucks to get the
good stuff.