You basically need a few conditions to be met to make this useable: tide needs to be high enough, there needs to be suitable geological formation that enables building of such power plants, it has to be publicly acceptable to build there, and you need to connect it to the grid. The last two can especially cancel eachother out.
However, this assumes you use potential energy. What you are envisioning might be more like current power (so kinetic energy) where I’m not sure what the limitations are. Perhaps it’s not too practical to build huge plants underwater in locations with relatively constant current and connect them to the grid
I have. I would probably use my last phone for at least another year if it didn’t loose system updates. There’s too much important personal data (bank, photos, messages including medical info…) on the phone to risk using it unsupported. At least to me it is not worth it so I try to buy a phone with reasonably long support and buy a new one soon after the old one looses support.