Been many threads on this. A typical three- stage converter does not meet all needs for absorption timing. Eg the CW four hours might be too long or too short.
If you use a single stage charger set at 14.6, you want to control the time that is left on. If manual control is not convenient, a timer can be used to pick a suitable absorption time.
Mex likes the household type of lights timer on the 120v side. Some fancy chargers will let you set an absorption voltage and an absorption time.
I thought this gizmo is an attempt to insert that fancy feature into the DC side of an ordinary charger.