Not everyone is aware that our brake reservoirs are calibrated to contain the amount of fluid needed to displace the pad wear both front and rear, between the min and max marks. There should not normally be a reason to top off the fluid unless a repair to a leak has been made, bleeding done, or all pads have just been renewed. If it is kept up between brake jobs, the function of the fluid level sensor as a warning for pad wear will be circumvented.

My personal take on the "synthetic" label is that the word has come to be a synonym for "premium" on the store shelves, much like "gluten free" is boldly claimed on foods which never had a chance of offending a Celiac patient. I believe all brake fluid is "synthetic."

Stack exchange discussion: https://mechanics.stackexchange.com/questions/13008/mixing-dot-4-with-dot-4-synthetic
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Art Benstein near Baltimore

If you have a lot of tension and you get a headache, do what it says on the aspirin bottle:
"Take two Aspirin" and "Keep away from children"