First off, please don't think I was insinuating your cheap as I was not.
I agree it is confusing with all the options, anecdotal internet info and marketing hype.
I use the H2Ocean because I like the fact it is an evaporated seawater based salt, but this means it will have some organics in it.
What do you mean by caked with clay? What colour is it? Does vinegar or bleach remove it? I usually clean my mixing tub every 6 months as it builds up a brownish residue. It is a Rubbermaid 300 gallon fiberglass tub. I also mix the salt in a 40 gallon glass aquarium and I do notice an organic build up but it wipes off with a wet cloth.
I think that since you are testing the main parameters you will avoid a lot of potential issues. I would also test for ammonia and if the batch is cloudy after 24 hrs I would not use it. It should also not cause the tank to go cloudy.
It's good logic that if you have to add stuff you might as well go with the cheap reliable salt, but there could be other deficiencies. In my search to replace IO I tried a new Reef Grade Salt from Thailand that was being introduced to the North American market. A friend recommended it so I tried it. I had a 10" tort rtn the next morning and all the acros looked horrible. This was after a 20% water change. Turns out they forgot to put potassium in the batch. I did over 600 gallons of water change in 24hrs before the system stabilized enough to put the acros back in. I learned my lesson from that experience and now stick with a high quality salt and test it before use.