Actually this one is compatible with my kit, I believe.

What does the manufacturer of the control handle specify? Typically valves and the plumbing attached to them do not have generic, mating fittings, are not interchangeable among brands, and have different requirements for how deep the valves are set in the wall. Because of these things, you can't just swap out parts and expect the result to fit together. Even when buying from the same manufacturer, you will find that not all of their valves can be matched with all of their fixtures.

It’s MOEN. I’m just wondering why my GC and PM want me to buy a new shower kit instead of a compatible shower valve.

Stop asking everyone else and do your homework. Go to the Moen site, find your shower trim and Moen will show you the compatible valves. One or more will have stops.

You have put the cart before the horse.

The valve choice comes first. You also have tried to buy a dysfunctional shortcut system instead of designing a system out of quality individual parts that are needed to do it the right way.

You need a thermostatic, not pressure balancing, temperature control valve with stops, and then a separate 3 way transfer valve to direct water to water to the tub, shower head, or hand held. Then you need a drop L, hose, bar mount, shower arm, shower head, and tub spout. All individually selected. Box store kits are poor quality and just like your contractor, I refuse to use them. I send clients to the local plumbing supply house, where they can find something quality that I’m willing to put my name on and warrant.

Cut them open yourself if you are a skeptic. But you are asking for callbacks if you allow a customer to pick that off the shelf stuff. I control the choices if I am expected to warrant a job. A homeowner doesn’t get the chance to give me wavy irregular tile and plastic parts. I do not need that kind of extra work for a worse result.

Frank and Frank-

If you buy a name-brand plumbing fixture at a big box store it will be identical, inside and out, to one purchased at a plumbing store if it has the same model number/UPC. The idea that name-brand manufacturers would risk their reputations by manufacturing two products that appear identical, but put inferior internal parts in the ones sent to big box stores, is an urban myth. The only difference is typically the lower price at the big box store.

Box stores used to sell ”the same” fixtures on the shelf as plumbing supply houses. 30 years ago. Then they figured out they could commission one off exclusive models to them that were far cheaper than their standard products. So that is what their shelves are stocked with. Exclusive models, with stand alone model numbers, that are made to their dollar demographics.

If you special order the same exact model number that a plumbing supply house sells, then then, of course, it is the same model. Those standard models isn’t what is on the shelves though.

Yes, you can find lower quality stuff on big box shelves, but I've also found standard quality fixtures as well. And, when I've special-ordered, the big box stores are at least as fast as a plumbing supplier. Like anything else, people should do their homework and compare model numbers and warranties.