Note that they explicitly did it with the intention of clamping down on informal breaks, socialising and other "distractions". The founder heavily suggested he decided on this solution because he wanted to cut down on on-the-clock use of Facebook, private conversations, etc. They basically enforce a rather strict work focus during those 5 hours and justify it by offloading that overhead into leisure time. Also the 5 hour cut-off is socially enforced with a strict "countdown".

Our company is in the same region of Germany and we independently started experimenting with our work time but our focus was employee well-being via stress reduction and encouraging our employees to use the extra free time for self-care.

We ended up with a flexible 25-40 hour work week (or similar 60-ish % adjusted for non-40 hour positions). The goal is to keep each employee's work hours as close to 25 as possible but allow for "overtime" (up to the full 40 hours) if necessary. If we notice employees are working "overtime" over a longer period of time, we rebalance the work load or adjust timelines as possible to get them back to 25.

Despite the reduction of work hours by 30-40% the effective work output only shrunk by 10-20%. But the real benefits are social.