"Is there any merit to their claim offering a legal way to play multimedia in
GNU/Linux?"
Given the wording in the FAQ they likely pay money into the patent protection
racket, thereby supporting the very problem that the free world seeks to
eliminate. In addition, my research online seems to indicate that Fluendo may
also be members of the DVD Copy Control Association, perpetuating another
problem.
Fluendo seems to be saying that the only way for people to be "safe" is to
pay for their proprietary software licenses so that they can keep you safe
from those that mat otherwise do you harm. It seems like the very definition
of racketeering and overlooks the two-prong strategy that the free world has
been pushing for to accomplish the same thing while protecting people's
freedom: The first prong seems to eliminate software patents entirely while
the other seeks to promote the use of formats that are not encumbered by
patent problems until (or unless) the first prong is successful. There is
also a third prong which seeks to eliminate DRM, along with various
DMCA-style laws in countries around the world.
It is important to reject their stuff, both to avoid supporting the very
thing that the free world seeks to eliminate but also for your freedom's
sake.