Very similar but as of today it doesn't have a backup sensor like tje tunze (float sensor is the backup). I read somewhere elos will be adding one in the future.
More in depth differences:
Sensor: Tunze uses an optic sensor, elos uses a heated prob. Both sensors work very good and are very precise.
Tubing: Elos uses a bigger tubing a doses bigger amounts of water, so if you use Kalk in you ATO tunze would be better as the water will be dosed at a slower rate.
Start-up: Tunze runs almost instantly after plug. Elos takes about 5 min which is the length of the diagnostics check run.
Safety sensor: Tunze uses a high float emergency for an added level of safety (the pump will not run if the sensor is raised). Elos rely on 1 sensor only.