Looking to add to the equipment collection and considering either the SMC-3 or MFO-1 (already have the MFO-3!). I know they are designed for different uses, but from your own experience, is one or the other more useful. For macro, I have the Sony 90mm (on A7C) and have CMC-1 and 2 for use with the kit 28-60mm lens (and they work great), but at times getting a little more magnification on the 90mm without a TC would be nice. Otherwise, having extra depth of field and less hunting on the lens make the MFO-1 a good option. Couldn't find a good thread for both of these lens, so I'm just looking for opinions.

It depends on how small a subject you find and want to photograph, the MFO-1 reduces the frame covered from 36mm wide to 30mm wide providing 1.2x magnification. The SMC-3 gets 2.3x with the frame being 15.5mm across with 47mm working distance. The SMC3 focuses between 47 and 103mm and I expect it won't give you any overlap with the MFO-1 range.

For me I would also factor in how often I find these things, if it's once on the entire dive trip maybe a better solution for this one critter is to crop?