Master buys component parts from the part manufacturers as their distributor OR from other distributors. Manufacturers are Clack, Fleck, GE/Autotrol, the resin and tank manufacturers or various manufacturer distributors.
I buy from the same distributors, dealers can not buy from the component part manufacturers.
Then Master assembles the softener or filter and sell/ship them to the plumbing/pump supply houses they market to. The supply house then sells it to the plumbers and well drillers and pump guys that sell it to the consumer; their dealer but they call them 'contractors'.
The "dealer" is responsible for giving their customer the manual and all other information necessary. Note this is a local dealer type sale, and if the customer doesn't get satisfaction, its the dealers' fault, not the distributor's or the supply house they sell to.
On average plumbers are pretty bad about these things, and only a few plumbers will be involved in water treatment sales. My advice is to go with a local or online water treatment dealer, usually water treatment is our only business.
On average, supply houses aren't much better than their 'contractor' plumber or well driller. Mostly that's because they usually do water treatment as a side line and in this case rely heavily on Master. Master has been doing this for at least 40 years and are pretty good at it but... they do not want to hear from anyone other than their customer, the supply house.
Master and the part manufacturers are not set up for their distributors' dealers or the dealers' customers to contact them. The whole industry is that way. My suppliers and the component manufacturers do not want to hear from my customer and the manufacturer doesn't want to hear from me. I am supposed to know what I'm doing and lean on my suppliers and take advantage of the schooling they and the manufacturers provide.
You are relying on information given to you by guys here and at that link that really do not know this industry very well. One is a customer of mine and another is a Kinetico salesman. The one giving the Master contact info is a softener owner. Another here is maybe a local and online dealer but doesn't sell what he says is the best equipment and says he is an installer as he was for Rainsoft for 20 years... None of the first three are a dealer or distributor or employee of a part manufacturer....
I have spoken to most component part manufacturers, Master and their field guys and supply houses as a local and online independent dealer for other distributors than Master for 21 years. I could call any of them and they would at least listen to me and help me depending on my approach and how I frame the question but they don't like the contact.
I've been donating my time answering posts like this for what will be 11 years the 2nd of next Jan and can tell you that the internet is full of good advice like... if you want to be dependent on a dealer for service, buy local. If you want to be independent and self sufficient then buy online.
As to what softener... IMO the best is a correctly sized for your peak demand SFR requirement based on your family size and number of bathrooms and type of fixtures, and your water quality; using a Clack WS-1 control valve.