I've used both. I think they are both fine. I don't like any pickups, so I have caveat and say that "fine" is high-praise from me. They are both stable and predictable.
The Realist is very consistent amp to amp, room to room with or without a pre-amp. The Full-Circle is a little more particular.
The Realist is "woodier" in an ideal setting and "swampier" in a lot of places and settings in which I play. The Full Circle is sonically more capable pickup in most settings, in my experience.
The Full Circle doesn't can't mark or damage your bass, but the wire is much more fragile. It can't practically be installed or removed without a luthier or someone really good or lucky at working on their own bass.
The Realist does mark your top a bit, but is better constructed in my opinion, the wiring is solid and reliable. I've installed it in a set break. It's very easy to live with.
I'm currently back to a Realist after trying a lot of things. I'm remembering what I didn't like about it in the mix sometimes, but I am basking in the plug-and-playedness of it. I don't think about it.
I have something new that I'm testing that might replace it, we'll see. I would go back to the FC if that wire/lead plugged into the adjuster wheel and was removable/replaceable when not in use. I'm not likely to go back to it otherwise. There's a much more expensive similar pickup only available in Japan that does just that. Maybe it will come here and price competitively some day.
Aside from that I generally agree with every other impression on this thread. You're not going to make a mistake either way. I think they are among the better choices for most people looking to plug into an amp....but I don't like any pickups. They're nothing more than "necessary" to me.