pHin will work perfectly well in a large residential pool. The only thing to be aware of is that your pool may require more chemicals than are included for free as part of your subscription.
There are a number of factors that impact chemical usage other than the size of the pool, such as the number of swimmers, the weather, whether or not you use a cover, etc.
For these reasons, we can’t confirm right now whether you’ll have any extra charges until pHin gets in your pool and learns about it. If pHin determines that your pool will need extra chemicals, we’ll contact you to discuss options.