My personal experience is a monthly saving of approximately 150kW to 180kW on my dual Solar geyser solution, and an average of 200kW to 150kW on my 5.5kW Deye, which has 2.7kW PV and 2 by 5kW Lithium batteries.
My Water heating system has made an ROI with in 4 years, and bear in mind that I get 300L of 65°C of hot water 320 days a year, with a average consumption of 1kW a day from the grid as a backup for the rainy days and over consumption of hot water.
ROI on the inverter is going to be more like 10 years.

Inconvenience does not even come into the equation. Seamless operation during frequent power losses and load shedding.