Before you get all wound up about risetime, be aware that risetime tells you nothing about the bandwidth on an oscilloscope. When using risetime the assumption is that the 0.35 number is constant for all oscilloscopes. Unfortunately it isn't. The only proper way to measure the bandwidth of an oscilloscope is to sweep the input using a levelled RF generator.
I wouldn't say nothing. Neither would Tektronix. Neither would physics. It's not absolutely accurate, but it will let you find out if your FNIRSI is more like 30MHz than 100MHz or your SDS1104X-E is more like 120MHz than 100MHz.
Of course the proper way is to sweep the frequencies, but not everyone can afford a 500MHz AWG to check out their 200MHz scope. However, they could probably swing $5 or $10 for a handful of readily available components and a PCB.
A small few of the folks around here (
) are not fixing heart-lung machines or calibrating self-guided nuclear missiles. They just want to have a little fun with electronics and their lab kit. Knowing the BW or their $600 scope to +/- 10% might be enough.
All that said, please rest assured I'll check myself before I wreck myself and not get too wound up.