I assume the Flexpreis allows you to take the train at any given time on the designated route, correct? That sounds appealing because 7:52 seems so early when recovering from jetlag, risk of oversleeping, etc.
But I noticed that some of the options say "High demand expected" and others say "Very high demand expected". How is this route on a Friday morning - would you reserve a seat (and therefore lock yourself into a specific time departure)?
Also, can you buy Flexpreis in First Class? If so, would that give you the best of both worlds (flexibility and a seat guarantee)?