I have said before, I had an iboost+ installed when I got solar, which I think is another version of what you show.
The result was it actually shows how much energy used. It shows saved today, yesterday, and last 7 days, useless this time of the year, not enough solar, but in the summer was surprised to see how little power used to keep the DHW hot. The immersion heater only heats up the top of the cylinder, so really not like for like, and the oil boiler is two floors below the cylinder so a fair bit of pipe work to get hot, and since C Plan quite large pipes, but to get warm water in summer, not really hot enough to kill legionnaires, but OK for washing hands, I would run the boiler 4 times a week, ½ hour each time, it would normally turn off after 20 minutes, so estimate using around 25 kWh per week.
The electric showed using around 3 kWh per week, so around £4 per month at peak rate, off-peak around £1.20 a month, clearly depends on how much used, we only wash hands, shower is electric, winter can't turn DHW off, so electric not used.
When I consider all the pipe work boiler to cylinder, and the fact the boiler also gets hot of course, not surprising that less electric is required to oil or gas.