There's a short thread about it here
mystery tripod bridge
The only bass I saw one on had bad varnish damage from the metal feet, but it hadn't pushed through the top. (but the soundpost had)
The rear foor was adjustable as well, bringing the bridge top forward or backwards as you liked it.
I guess the theory was that instead of adjusting the soundpost for sound, you could experiment with the bridge angle, position and pressure. I suppose it didn't work out.