This study measured the effectiveness of an isolated lumbar extension machine and kettlebell swings and their ability to fatigue the lumbar extensors (lower back muscles), thus showing particular exercises work those muscles.
​I feel this has particular relevance in Brazilian Jiu Jitsu (BJJ) because lower back pain can be a common complaint from many BJJ and grappling practitioners. Whether caused by the sport or not, a big factor may be the constant flexion (or bent forward) position you see in the spine when in many positions. Strengthening the lower back once you've recovered from the initial injury could help prevent further problems in this area.
Are one armed kettlebell swings better for Jiu Jitsu?
Well if you're short on time and want an exercise that develops better core strength through causing instability (which is probably more specific to Jiu Jitsu) then one armed swings could be a better option to have in your program.
The results of this study may be fairly intuitive, although backing up what you do with real results is important. It is one of the first, if not the first, to see the differences in muscle activation between one armed and two armed swings.