I’m a long time user of a Nauticam flip holder for a single wet diopter. Usually starting a macro trip with a +5 SubSee before switching to an SMC-1.
The discussions about the MFO-3 make it sound like a great lens to have around when geared for macro (Nikon 105VR).
I learned a long time ago that trying to screw lenses on and off underwater was NOT a task I favored.
A double flip looks super bulky, appears to add a lot of front weight, is a bit $$$, and the length of the MFO-3 doesn't seem very amenable to a flip holder.
I have reason to move to a Nauticam bayonet mounting system for other reasons.
But - The pricey arm holders for extra lenses on bayonet look like they again add a lot of front loaded weight & bulk.
I do have a large front velcro pocket on the waistband of my backplate/wing as an option to store the lenses when not in use.

What are folks’ experiences with wet swapping lenses using the bayonet system from Nauticam?
How do other folks carry around the various lenses for macro shooting while on a dive? 

I'm using a bayonet holder for my MFO3, I'm on m43 so the magnification of the 60mm macro lens is sufficient and I don't use a diopter. So only taking the MFO3 on and off and not needing to park a diopter.

Swapping them is fairly easy, the MFO3 is a heavy lump above water, but doesn't give me problems below water. I also used cargo shorts when diving in Lembeh, I only needed to fall off the boat so no issues with them falling down, not an option shore diving in Sydney where I use the bayonet. The bayonet holder is mounted on a strobe arm, when I'm entering/exiting the water I have the neoprene bag it is supplied with covering the lens. Getting washed into the rocks exiting is a common enough occurrence that some protection is needed. Once UW I remove and clip off the bag.