I use it quite often... It is actually quite good up to some 500ish MHz, and has 10 Mohm input resistance combined with 0.5- 0.6 pF input capacitance..
I terminate it to 50 Ohm on scope side, and have a custom probe defined for it.
So, as a 1 GHz FET high impedance probe is not very good. As 500MHz active FET probe is great bargain for money...
P.S. Putting it into metallic case and good grounding will flatten frequency response... If one would want to play with it, compensation network could be made to flatten it more... But up to 500 MHz it's not really necessary .. Using passive probe would be much worse...