I think the real question is, “is the Framemeister worth it” (since it’s the more expensive option).
OSSC is cheaper, has less lag in scaling images.
Framemeister has more image adjustment options (currently), and apparently supports some non-standard resolutions — especially useful for some arcade PCB’s.
I own a Framemeister and am waiting on my OSSC 1.6 to arrive to make a proper comparison. But for me, I play mostly action-based games and the lag on the Framemeister makes some games hard to adjust to.
If the OSSC turns out to be as lagless on my set-up as it claims, I’ll be very happy.