the 90gr xtreme-defender 9mm projectile is a bit light, might not generate enough recoil energy to reliably cycle the R9's action. I have not tried any , thought. To me, 124gr Gold Dot seems capable enough and is a bit cheaper.
My very limited experience with underwood ammo, so far: I have some xtreme-defender underwood in 10mm, spec is 110gr @1700fps / 738 ft.LB so it is supposedly a pretty hot load, but the felt recoil in my G40 is very very manageable, about the same as my practice ammo (S&B 180gr FMJ, ~540 ft.LB); in comparison, the Sig v-crown 180gr JHP (spec is ~650ft.LB) is quite a bit more stout.
And the xtreme-defender 10mm underwood, shot from my G40, appeared to be VERY accurate, it grouped tighter than the Sig V-crown.