Suunto D4f

The programmable depth alarm. You set a target depth, say 20m, and the D4f beeps when you reach it. For training sessions where you're trying to hit specific depth targets repeatedly, this removes the need to check the display on every descent. The ascent alarm (beeps if you ascend too fast) is the second most valuable feature for safety.

The D4f automatically tracks the time between each dive in a session. It shows your current surface interval on the display. For following the 2:1 rule (rest at least twice the dive time before the next dive), having this number visible on your wrist removes the need for a separate timer.

If you use programmable alarms and care about a detailed dive log: yes. If you just want depth and time tracking: the Cressi Newton at $150 does that at less than half the price. The D4f's value is in the alarm system and the companion app data. Divers who don't use those features are overpaying for the brand.

No, most recreational divers never exceed 40m. The 100m rating means the device is built to a higher pressure spec than strictly necessary, which provides durability margin. You're not paying for depth you'll use; you're paying for build quality that won't fail at recreational depths.