The Easystart Select has a display and error code reading so would be a good solution for your Airtronic M D4 Plus (H-KIT).
Maybe also the Easystart T would be a solution if you wished for a timer function
https://www.butlertechnik.com/technical-library/eberspacher-easystart-t-7-day-timer
Both controllers would require replacement of the existing heater harness plug and electric terminals ( these are included within the box)