I owned a pair of Royer SF 1 mikes for a while; they're the single-channel counterparts of the stereo models that you're talking about. They were very good microphones, and I found Royer's customer service and support to be first-rate in all respects.
The fragility factor is something that I personally could never quite get comfortable with. I record professionally; my microphones must be reliable and consistent for hundreds and hundreds of recordings over years of use--including some where recording conditions aren't entirely predictable. In 2,000+ live recordings I've had only two microphone failures that I can recall (both in equipment that I'd bought second-hand), and I want it to remain that rare an event.
The other problem I see is that a figure-8 pattern is really not a good choice for one's main or only microphones. I like using crossed figure-8s ("Blumlein" stereo) where I can, but there aren't many situations where all your sound sources fit well into the relatively narrow < 90° angular range that is the absolute maximum for Blumlein. Since figure-8 microphones are fully as sensitive in back as in front, you can't move farther away to encompass wide sound sources, or your recording will be swamped in room reverberation.
In the end while I liked the microphones, I never found them to have any special sonic magic. Despite all the claims people make about ribbons, their frequency response was no smoother than that of my best figure-8 condensers either on- or off-axis, nor were their polar patterns better controlled (e.g. their famous supposed lack of off-axis peaks). Their low-frequency response was better (which would be very nice for M/S), but their high-frequency response rolled off at 11 kHz. I've been amazed to see inexpensive Chinese-made ribbons being taken seriously when their response extends to only about 6 or 7 kHz before rolling off (and that's in the published specs; who knows what they really achieve).
--best regards