The digital display/controller I have has 4 buttons - 1-fan only (I don't use this), 2-on/off, 3 & 4- temp up and down. My methodology is to turn on at 4-5pm at 20-22C depending on how I feel. leave the ensuite open while cooking and doing the dishes, so the shower area warms up. Once showered (and perhaps not every day depending on water supply) I close the ensuite door.
When I go to bed, I lower the set temp to around 13C and let the Doona do the rest. This causes the heater to "go to sleep" or if easier to explain, turn off. When the temp in the van goes below 13 the heater comes back to life until it gets warmer outside. This can happen at 1 am on a really cold night or 4-5am when milder, in other words variable.
I turn it off once I'm out of bed and dressed. This usage in hours is around14-16 hours, the heater averages 1AH when it's ticking over and my average use is around 12-13 AH. Diesel usage is variable also depending on set temps and ambient outside but my average is 1.5 lt a day, sometimes 2 lt again when colder.
I can not speak to the Chinese or Russian knock offs re control, but have met several people that have had non start issues among other problems.
Re size, my van is a single axle ensuite at 18'3" a 2kW is ample for that and up to 20-22 footers. My van is also very well insulated and this also makes a difference. I know some that have put a 5kW into a smaller van than mine, their diesel use is higher and re battery use, I have 3 mates that have had flat batteries next day or heater cutout due to low volts. To be fair that was because their battery system was less than good to start with and the heater is the thing that pooped the "Camel"
Let me know if you want more info....