I am a great fan of Tylers and and Magnas, but NOT on an aluminum J-frame RB, even for standard-pressure ammo. I wouldn't shoot +P in ANY aluminum J-frame, including one rated for .357 Magnum. It's not about pressure, it's about recoil.
YMMV. I know one very knowledgeable gun-rag writer and retired police chief who DID like a Tyler and Magnas on his 642. For me, it just caused my middle-finger knuckle to get rapped by the trigger guard.
P.S. For me, Tyler and Magnas ARE OK on SB aluminum J frame with standard-pressure ammo.