Does the DD30 work without the app?

Yes. You can run it from the unit itself. The app adds scheduling, remote control and status checks, so it is optional rather than required.

How does dual drainage work?

You can let water collect in the tank and empty it, or attach a hose for continuous draining into a drain or bucket. Continuous draining suits basements and unattended use.

Is a compressor dehumidifier right for a cold room?

Compressor dehumidifiers like this one work best in warmer rooms. In unheated spaces that stay cold, a desiccant dehumidifier usually extracts water more reliably.

How does it compare with a plain mechanical dehumidifier?

The main difference is the app: remote control, scheduling and monitoring. A basic unit does the same core job of pulling moisture from the air without smart features.

Shoppers with a damp bedroom, basement or small flat who want to set schedules and check the unit from a phone. For whole-house or very cold spaces, look at larger or desiccant units.