Both my kids use out keyboard a lot. They only play a piano at lessons, and I can't say they are troubled by the difference at all.
I recommend getting one that has sound effects. My kids use the keyboard a lot more because they can play "Ode to Joy" with barking dogs or guttural grunts or gunshots. Ah, the joys of having boys...
It's nice that the keyboard is portable so that we can take it on vacation and such. They love getting to "perform" for Grandma!
The one drawback to our keyboard is that it doesn't have pedals, so there's no practicing anything requiring those. But it's a trade I'd make again, especially for the price. Keyboards are a lot cheaper than pianos.
