What does ATC_RAT_RLL_FILT do?

I’d like to know how to explain and use it (ATC_RAT_RLL_FILT)

That parameter doesn’t exist in 4.0 where you have posted.

In Copter 3.6 it was ATC_RAT_RLL_FILT and from Copter 4.0 onwards the filters were expanded and the equivalent is ATC_RAT_RLL_FLTT

Use this spreadsheet, or the Initial Parameters section of MissionPlanner to calculate values for your copter

The use of some of these parameters is explained in the Tuning guide

And in the Full Parameter list

It applies a filter on target rate. So if you are giving very noisy inputs to the controller, it will filter out some noise depending on the Hz.

Is it better if the price is higher?Or is it better if it’s lower?

As I said

and follow the tuning guide