I despise hydrominders that are hard plumbed in the tank below the lid.
When I designed it originally, they wanted the smallest possible footprint for the tank, so I measured and had the tanks make so a Hydrominder would just fit and operate properly. The only modification to anything was to put a longer nipple between the two street elbows between the valve and the eductor so the chain could be removed completely and the float weight hooked directly to the wire to maximize tank volume. It's very easy to service the valve in the tank. I hate the valves clamped to the tank edge because it's a pain in the ass to service the seals, and the tank gets crap in it (Crickets are a huge problem here every few years and they get into everything). The worst part is that you have to pull the Hydrominder out to change the tip, but how often do you have to do that?
All the systems we installed had
Flojets. They work fine, usually last three years or so with Viton, rarely more than a year with Santoprene. I've set up a few for customers using Procon and it works about the same, just slightly longer changeover time with the extra plumbing of the regulator and bypass.
I've done both 1/4" and 3/8" tubing on installs, I choose 3/8" if the option is left to me, but at 70 PSI on a
Flojet I can't tell a difference unless the longest run is over 100', which it has been.