PPS is no less costly than EI or any other DIY based fert routine and it is certainly not less expensive that a non CO2 method or sediment sources of ferts.
The DIY ferts are all less expensive than Commercial brands.
EI can also be done with or without water changes if you want to as well.
This isa non CO2 method, I use about 1/10 th EI and do few if any water changes, maybe once every 3-6 months?
Here's a tank with CO2: once a month water change:
Here's one that's been getting 1x a week:
EI nor any method is rigid and the user can add more or less as desired.
I start high and then slowly reduce and watch the plants. Common sense.
This way you know the plants are not limited as you reduce and can see the 1st signs. If you start at a limiting level, you have to reference and the plants take longer to fully recover if the dosing is too low.
This same idea is true for every method, not just PPS.
In fact, sdediemtn based ferts systems are better and no dosign is required or even less to the water column for longer extended periods.
But realistically, we dose the fish and dosing as long as you somewhat consistent... is not critical. Light/CO2 and your own management are larger factors.