I guess it depends on the design and implementation of the two pieces.
My only experience is with Really Right Stuff L-brackets but my Z9 bracket is every bit as stable as previous versions for other Nikon bodies. It's vertical bracket slides into the base and is secured by its own set screw.
I've used several L-brackets with removable side plates and never noticed any flex at the joints. But, as @JBPhotog noted, there are many different designs. It seems like a bracket milled from a single billet would have to be stiffer. But how much load would you need to apply to flex a bolted connection? The single 1/4-20 connection to the camera would probably flex or fail before the bracket's joint did.
Most of the two piece designs I have seen used a combination of bolts with some manner of tongue and groove shapes to interlock the plates. A flat face connection relying entirely on bolts probably would be more flexible.
One thing that did annoy me on at least one L-bracket was that the "L" segment bolted through the bottom of the base plate. So with the "L" removed, the base plate extended out beyond the edge of the camera body. It looked dumb and was uncomfortable if your hand was under the left corner. All the brackets I have today fit flush to the left edge of the camera when the side plate is removed.
I use 2-piece Arca-Swiss (clone) L-brackets with my two, small Canon M5 and M6 cameras. In both cases, the vertical piece can be removed, and you have the horizontal baseplate still attached.
I have a RRS BCM5-L 2-piece L-bracket on the M5, and something else on the M6 (probably Neewer or whatever was around then). Both of these two-piece L-brackets have been in use for eight years, frequently in the past couple of years. Never had a problem. I think I left the uprights at home for a trip to Europe, but they're pretty small. OTOH, all of my full-size DSLR had/have one-piece L-brackets.
jeffbuzz wrote:
... It looked dumb and was uncomfortable if your hand was under the left corner.
Thanks, guys. I'll remain aware of the comfort factor. My current MILC cameras (Sony, Nikon) have base plates from SmallRig and RRS, both to extend the grip and to mate with A/S clamps. I'm trying harder to keep my ball heads balanced but don't want an L-bracket for all my activities.
RRS uses an erector set design with multiple parts. I think it is practically mandatory on the larger pro body brackets or brackets for cameras with battery boosters.
