I've had some experience with the Donner DEP-20, and considering its price point, it does offer a lot for beginners. The weighted keys are pretty impressive for an entry-level model and give a decent imitation of an acoustic piano's feel. However, compared to brands like Yamaha and Casio, you might notice some differences, especially in sound quality and key responsiveness.
Yamaha, for instance, often invests heavily in sound sampling technology, which can make their entry-level digital pianos sound richer and more authentic. Casio has also been improving its digital pianos with better acoustics and features like their AiR Sound Source.
The Donner DEP-20 does feature multiple voices and a variety of settings, which are fun to experiment with, but it might not reach the same level of tonal quality as a Yamaha or Casio. It's durable enough for a beginner, but if you plan to advance or are particular about the nuances in sound and feel, you might eventually seek an upgrade.
I recommend testing it out, if possible, alongside models from Yamaha and Casio to see which feels right to you. Each has its strengths, so it really depends on what aspects you prioritize. Have you had a chance to try any of these pianos in person? I'm happy to help further if you're interested in specific comparisons!