These old JFET probes (from Tektronix, HP, Philips...) not only have a low bias input but also a very low input C, which is what makes them really useful in HF measurements at mostly any point in the circuit.
However I'm amazed at the high input C of the hyperexpensive tektronix IsoVu (starting at 41dB$ according to the X-chapters), 20pf at 1MOhm with no input divider and 0.5V range, there goes all the bandwidth