Pre-set ones tend to be more restrictive and limit flow
Adjustable ones have higher flow ratings
Personally I use an adjustable set to 50#.......fill my fresh water tank and exclusively run off of pump. Constant pressure and flow regardless of where we go.
PLUS I don't have to worry/deal with a 'flood' like the one that happened in 2008 when on city water with regulator and fitting gave way while we were sleeping .....flooded the RV to the tune of $6000 in repairs/costs
No more city water hook up for us.
Fill tank use pump and with just a flip of the pump switch turn it off at night or whenever leaving RV evn when just gong outside......SIMPLE