Well I am in Canada EAH?
I do not get it from BIG BOX places, marine supply if I am in a bind, or specialty plastics type places have better prices.
I seem to like "industrial formulators products" It was a local company but got bought by system 3 in the USA I think. "System 3" sometimes, "West system" (the "benchmark" company for boat building, but the price is more) "East System" is good
Using different epoxies, one on top of the other, is "probably" ok, but the manufacture will never tell you that.
Bondo over epoxy or the other way around, let the product reach full cure time times 2 before putting different over top.
There are 2 words that are used, hard, and full cure, better instructions will state that, and then tell you it changes with temperature. (in other words, you figure it out
Products that are 100% or very near 100% solids is better.
I use epoxy mostly because I am more familiar with it. (it does not stink like polyester (bondo like product)
Bondo makes more sense due to price and availability. (Not every thing I do makes sense