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In the 90s I had a Roland EP7 in addition to my acoustic piano. I used the EP7 for silent practice. I eventually concluded that practicing on the EP7 was actually doing damage, and that I'd be better off not practicing at all!
Digital pianos have come a long way since then (and even in the 90s there were much better digital pianos than the EP7 available!). Previously I owned a Casio PX-330, and a few years ago I replaced it with a Kawai ES920. With both of these I can work on my technique on the digital and the skills I develop transfer nicely to the acoustic. The experience of playing is more satisfying on my acoustic piano, but for learning piano skills, at least at my level of playing, I think the digital piano works almost as well as the acoustic. It's really nice to have the flexibility to practice anytime without disturbing anyone!