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Demand Hot Water circulators are GREAT Retrofits if you wait for hot water.
1) Put one under the most used bathroom vanity. Connect to hot and cold faucet risers with 2 Tees. No plumber required, only an adjustable crescent wrench and tube cutter.
2) Plug the pump into the GFCI outlet.
3) Push the doorbell button for a short (20 to 90 seconds) pump run. When the motor stops, hot is HOT and cold is COLD. The shower and any other fixture on that water riser now has hot water.
Not a drop, cold or hot, is wasted.

I am very happy with my 2 year old Chili Pepper. It definably saves water and and it hard to imagine it does not save electricity - lost after the shower gets hot and before I notice it.

Look at RedyTemp and Chili Pepper. I don't see others that are as popular.

I really don't like the timer pumps (Grofundos?). I get how they work but I don't see the convenience or energy savings. And they do require a plumber, and perhaps an electrician.

"Blower door guided whole house air sealing" and duct system sealing using AreoSeal qualifies for tax credit when the contractor reports in writing the test-in and test-out CFM's --- which yields the % reduction in leakage. Like adding R value, measured leak reduction counts for tax credits. This was interpreted for us by IRS.