The Rhea doesn't actually require soldering as Dominik will do the soldering first before shipping. For sure having to know 20 versus 21 pin is a pain. But the Rhea/Phoebe have a huge advantage of being here now and known to be very reliable (they work flawlessly). Not discounting this new approach, it seems very promising, but just pointing out there's already a solution available today for those who didn't realize.
The nice thing about this new solution, even ignoring that it furthers public understanding of the hardware, is that it's a simple module that plugs into a slot already available and accessible on every Saturn ever sold by SEGA (presumably it won't work on the Hi-Saturn units made by Hitachi, as they had the MPEG hardware integrated, though they are also very rare and very expensive).