These have good low frequency specs., and the negation of having to have electricity or air, is a bonus
in some applications. I still use air suspension for my
low frequencies and then an interferometrically feedback controlled piston/servo/piezoelectric combo, for the higher frequencies.
Finally then... I modelock my fringes, and use
two photon injection to each cavity, through a distributed
phase matcher. I guess my requirements are a little bit different than the norm?