The Mous seems pretty legit. Just looking at the design it’s obviously highly protective. There are a few YouTubers who have done some pretty dramatic drop tests which basically back up the Mous ads:
These are older models, but the tech hasn’t changed much since then.
UAG rates their Monarch for 25 feet. If you hunt around you can likely find some drop tests. It seems to be at least as protective as the Defender.
Filip at EAP (Phone Rebel) does an annual 50 foot drop test. He hasn’t done one for the iPhone 15 yet, but he did one last year for the iPhone 14:
Ironically, both the Defender and the Monarch failed this test. His Phone Rebel and the Mous both passed, among others. At these heights, some of what determines the outcome is due to luck.
I think the Defender is a fine case, but it’s perhaps more bulky than it needs to be. It was arguably the first case that built a reputation around extreme protection and I feel like that narrative has stuck around even as some modern designs that are slimmer offer similar, if not superior, protection.