I have been following them for a few years and they are making some slow and steady progress
From their page: As the world generates more electricity from intermittent renewable energy sources, there is a growing need for technologies which can capture and store energy during periods of low demand and release it rapidly when required.
At Gravitricity we are developing innovative, long-life, underground technologies which store energy safely and deliver it on demand at a lower lifetime cost than current alternatives.
Currently, they are specifically advertising that they can provide really large amount of power for very short time. I don’t know where I read this but CERN is storing discharging some big capacitors to jump start LHC, and gravitricity can provide same power by parallely lowering heavier weights. source required