But my experience is: standard 10x probes over 250MHz will all be pretty much the same..
Don't look at bandwidth, look at capacitance at tip. Circuit loading will define what you will see in real life.
Yes.
Example 7pF with 300MHz equals roughly 75 ohm and with 500MHz roughly 45 ohm.
It need always remember that Lo-Z probe, piece of coaxial and resistor in many times far better than usual probe with high frequencies. Usually high freq circuits are low impedance circuits so this 1Mohm is nonsense due to tip capacitance.
Inside this article there is 1kohm probe... good to 1GHz and even up several GHz
it is not 1:10 but 1:21. It need connect to 50ohm input.
http://www.sigcon.com/Pubs/straight/probes.htmwell it first feel that 1kohm... blah... but this is for HF circuits.
We can think other way. Take some probe, example tip 7pF. What is frequency where its cap.impedance corresponds 1kohm. Roughly 22MHz. So with 22MHz or higher this 1kohm probe is loading RF circuit less and also it is more like resistive. Very usable and over 100MHz or exaple with 300MHz it beats normal probe hands down in many things. Is it difficult because it is 21x probe. Of course not. Just turn your scope probe factor to 21x or even more accurate just using some reference signal and probe factor fine adjust. And its price is... piece of RG174 and resistor and example small short pogo pins if want. "It must be poor because it is cheap"... forget this thinking. For what need fancy expensive 500MHz passive probe. For lower freq it is not at all needed, better use probe what is also low pass filter. For high frequencies cheap but ugly looking DIY Lo-Z may beat expensive probe hands down. And if bad happen... just laugh and make new. No need be sad when 100 Euro or 500 Euro was gone.
Of course these nice expensive probes are good for many things and in some cases better than diy LoZ. But is it wise first carefully think reality with probes and higher RF before open money book... buy roses to your wife and do 50 cent DIY Lo-Z or collect its material from recycling basket.