My very minimal experience with Zero Rust: I purchased a quart of grey ZR several years ago, likely from autobodystore.com as I also get my Picklex 20 from them. I thought I'd try it since the proprietor of autobodystore.com, along with others, were praising it at the time. Never again.
The ZR is high solids alright. Very heavily bodied. However, there are absolutely zero basic "how to" usage instructions on the can label except for very prominent "DO NOT THIN" lettering. What the ...? The stuff was so thick it wouldn't even brush well without thinning. About the only way ZR might be usable right of the can is with high pressure airless spray equipment.
I visited the ZR on-line site only to find that, yes, it could be thinned, and several acceptable thinning products were listed. However, there were no ratios given and the user was left to "thin as needed". Well, that information directly contradicts the label caution on the can! Unless one is used to using this product in a conventional automotive type spray gun, any thinning becomes somewhat of a trial and error process, not to mention the possibility of running afoul of any VOC regulations that might apply - if anyone cares about that.
I admit to being biased against a paint product where the most basic usage instructions are not provided by the manufacturer directly on the can label. That information should minimally include specifically recommended thinning product(s), if needed, along with appropriate mix ratios and any recommended or optional additives and their mix ratios. I find it very misleading to have manufacturer's on-line usage "recommendations" directly contradict, in a very fundamental way, what is specified on the can label. That's simply unacceptable to me and I have no use for any manufacturer that does it. ZR may be the best product in the world but I will never buy any more of it or recommend it to others.