Most comparisons focus on equipment and price. Two less visible items decide how much protection you have after the crew leaves: the warranty on each part and whether the installation was permitted and inspected. Both can be settled in writing before you commit.
Ask which parts are covered and for how long
A warranty is not one promise. Ask the provider to list separately the coverage for the tank or housing, the control valve, the media or resin, any electronics, and the labor. Ask how long each one lasts and whether the period starts on installation day or on the date of purchase. Ask whether the warranty is from the manufacturer, from the provider, or from both, and what happens if the provider stops operating.
Find out what can void it
Read the conditions carefully. Some warranties depend on the provider doing the scheduled service, using approved replacement parts, or keeping the equipment within the stated water conditions. Ask which actions would end the coverage, and ask who pays for the return trip when a claim is approved. A warranty that depends on a service visit you are not willing to pay for is worth comparing against one that does not.
Ask whether a permit is required
Plumbing and electrical rules differ by city and county, so ask the local building or plumbing office what applies to your address rather than relying on a general answer. Ask the provider whether the work needs a permit, who applies for it, whether a final inspection is required, and whether the drain or discharge connection falls under the permit. An installation that was never inspected can cause problems when you sell the home or make a later insurance claim.
Put the answers on paper
Add the warranty summary and the permit answer to the quote before you sign. If a provider cannot state the coverage or the permit plan clearly, that tells you something useful about the rest of the job. For how we look at provider practices, see our methodology.