Some information on why these 5-1 epoxies exist vs. the common 2-1 or even 1-1 mixes:

WEST was on of the first epoxies available to the common boating market to make it's appearance. 5-1 epoxies and even 6-1 ratio epoxies, are highly resistant to water infiltration. They were intended among other things to be able to withstand submersion in water without any infiltration into the desirable properties of the epoxy - such as boat bottoms. 2-1 epoxies can't equal those water barrier properties. I'm talking on a molecular level and not just assuming it resists water which all epoxies seem to do well. But over extended periods the 5-1 epoxies will far out perform any 2-1 or 1-1's. But for a sheathing and adhesive epoxy, the 2-1s are fine especially considering they usually get coated anyhow. I think WEST just came up with pumps to make mixing convenient for the home user whereas commercial users have scales.

One thing I give WEST a lot of credit for, is a very comprehensive information library available to everyone showing repair and construction methods with epoxy. Even other epoxy brands have learned from WEST.

There's actually 6-1 epoxies that aircraft builders use. I use 2-1s for convenience and lesser price. But I have used WEST quite a bit and was always totally satisfied but the pump and ratio thing is a bit trying.