I have one of the early .357 L5s, and it initially had some cycling issues. It seemed to be a design/engineering issue. I had contacted MRI, and they had me send it in. They ended up replacing everything above the frame with redesigned parts. The upgraded parts work fairly well. The only issue I have now is that the gas port in the end of the chamber seems to shave bits of bullet jacket when the gun fires. I have a photo posetd
here.
This seems to be a rare, but not unheard of issue with some DE barrels, and is not specific to the L5 models. None of my other barrels have this issue.
The L5 is noticably lighter than the standard MK-XIX, and the recoil impulse of the barrel with the internal brake is noticably different than the un-braked barrel. Not better / worse. Just different.
None of the major components are interchageable between the L5 and MK-XIX. This includes the barrel, slide, bolt, recoil spring assembly, gas plug, and maybe a couple others. If you're planning to get a bunch of different barrels, you might be better off getting the more common MK-XIX. But as a stand-alone gun/caliber, it seems to work well.