Read up on the links that Herman posted.
basically u want a swg that is rated for at least 2x’s your pool’s volume. So 20k gal or more for your 10k gal pool.
Bigger is better (the units take up the same space regardless of cell size).
Get the biggest one that’s in your budget.
The bigger the cell, the more fc it produces in 24 hrs. All swg cells have a finite life span of roughly 8-10k hrs @100%.
Oversizing allows you to run the cell less time or at a lower percentage to produce the fc u need daily- meaning the cell will live longer & u will have plenty of fc at your disposal.
For example- a 15k gal rated cell means that it is designed to adequately chlorinate a 15k gal pool if operated at 100%, 24hrs a day. This doesn’t leave much wiggle room & in sunny, hot Florida, with a long swim season the 8-10k hours of runtime will occur within a short time period & you would be replacing your cell.
The upgrade from 1 size to the next is generally a good value when compared to the chlorine output you receive over its lifespan.