One thing, and this will get most everyone's goat except for the chemists out there: there is an amine blush in no-blush epoxies. Blush is the waxy, slick feel to a greater or less amount on cured epoxy surfaces. It comes from, in the most part, from the interaction of atmospheric moisture on the unused amines in the two part mixture at the coat surface. Amines are nitrogen containing compounds that work to help cure the epoxy resin in a timely manner. Every epoxy outlet and distributor has a line of no-blush epoxies, but resins and hardeners all come from the same manufacturers aside from the claims of the sales reps (just ask for the MSDS and/or check Chemtrec). With the hardener can before you, open it up and waft with your hand some of the vapor to you. Take a sniff, but careful, it's nasty. Smell that ammonia smell? There you go, the source of the amine blush.

Blushless hardeners are actually well worth their money in that the formulation is exacting for the amount of constituents there are. In other words, better mixing and control. That said, last year there was a flood of totally bad hardener that affected several epoxy companies. Putting that aside, back to the way it is. Too much of the amines and the epoxy doesn't cure hard but becomes 'cheesy,' more hardener and it becomes gummy. Conversely, too little and it takes forever to eventually harden, if it ever does. It's an exacting science meaning better QA/QC at the mixing location.

Avoiding even trace amounts of blush:
To avoid any possible problems, amines are water soluble. After the first coat is cured, use some hot water and a green scrub pad and give it a good going over, then rinse. The trace amounts of amines will come right off. Some people like to apply a second coat or layer of glass in the later green stage. I've heard that minimizes an interface of amines. Frankly, in all my yaks, I was too lazy to do that. I chose the hard cure and rinse route, with a bit of roughening up the surface to insure a mechanical bond myself.

Bottom line that's nowhere near the bottom line:
The whole point of this is to know that "blushless" is a state of being that excludes the kind of epoxy we use. Hope this helps.

Health and safety issues:
If you can arrange it, epoxy in a well-ventilated area and don't waste your time using a air-purifying respirator unless it is fit tested, a full-face type, and has fresh HEPA filter element(s). Wear gloves, most people develop a sensitivity to one of more components within the resin or hardener parts. If you get some smeared onto yourself, don't panic, finish what you're doing and then use vinegar to wipe it off. A gallon of cheap white vinegar is a great thing to have around for spills and smears.

If you knew all this already, somebody else probably reading this didn't and it's for them, then.

Oh yes, I've used US Composites stuff and liked it, too.