The rise/fall time of the FETs is about 0.15ns which is calculated from its typical on state resistance (3 ohm) and load capacitance (50pF), so it could technically support into the GHz range under ideal conditions. However the circuit itself and connectors are definitely not designed for that. I am going to have some more in depth tests in the coming updates, but with what I have on hand currently, 50MHz square waves get through without too much attenuation and distortion (so say ~200Mhz bandwidth currently as a safe guess).