No issues with lockup 14 seems to be the sweet spot. Also yes it’s just a ismi spring .
My polymer pdp has a 11lb recoil spring , lucky 7 ports , reduced striker . As long as I keep it oiled it has no issues with lockup however most people will run 13lb . The steel frame without changing the striker will function fine with 15/14lb if you go lower you will have to change out striker to a reduced one to counter lockup.
best thing is to see what the gun will run then video it to the side see which one runs the flattest without to much muzzle dip etc .