As Valveman indicated, I believe this plumber for Lowes just didn't know what he was talking about.
Even my realtor said he had a few of his clients on city water purchase similar water pressure booster pumps to successfully increase their city water pressure.
I believe it wasn't until 1992 that the US government restricted shower heads to 2.5 gpm, and bath tubs to 5 gpm. It's worse in California. As you know, many people are desperate to quickly remove the water-saver out of a shower head when it's still possible.
Today, manufacturers have become wise and started making shower heads where you can't remove the water-saver. The new cartridges have built-in strictors that lower GPM so it won't even matter if you remove the water-saver in your shower head.
I don't see the point when it comes to filling a bathtub, as the tub needs to be filled regardless.
Prior to 1992, I don't recall hearing massive "blow outs" when water pressure was often way over 120 psi back in the day. Not to mention the links and videos I provided in this thread which clearly shows people enjoying their 100+ psi showers.
After I emailed the Lowes plumber the 5 items I wanted intstalled, he basically said it couldn't be done because I would blow out everything in my house. He basically made me feel like an idiot for suggesting it, and said it had nothing to do with "code." These were the 5 items I emailed him:
1)
https://www.homedepot.com/p/MasterS...lume-Control-and-Stops-K-2976-KS-NA/203782809
2)
https://www.homedepot.com/p/Kohler-3-4-in-wall-2-or-3-way-Transfer-Valve-K-728-K-NA/202388604
3)
https://www.rheem.com/product/resid...essional-classic-plus-series-heavy-duty#tab-5
4)
https://www.lockewell.com/index.php?main_page=product_info&cPath=1_3_86&products_id=1788
5)
https://cyclestopvalves.com/collections/frontpage/products/custom-pk1a-pside-kick-kit
Plus, I kept insisting I want a Rheem Pro water heater, and he always pushes back with STATE water heaters. I'm paying, so I should get to pick what I want.
Anyhow, thanks for the education I received on this website as I'm not a plumber and just a lay person. I'm still not giving up as this is America!