Jonpaul, you are quite right that an impulse/spike is not suitable for calibrating scope front end response, nor for rise time measurements. However, the standard sqaure wave pulser from Leo is actually perfect for transient response testing of most scopes a few GHz and below. Beyond that you start to need to consider the rise time and shape of this generator's pulse when interpreting the result. The small-ish 1 Vpp (terminated) voltage might be a limitation. This can be reduced with 50 Ohm attenuators, but then the response of the attenuator needs to be considered.
In the thread referenced by rhb
I demonstrated a way to directly determine frequency response of a scope using Leo's pulser. This requires that the scope has math-on-math capability. You display a single rising edge, then average many waveforms (remove noise, increase resolution), take the derivative d/dt (to get an impulse from the step), then take the FFT of that impulse. The displayed FFT is the actual frequency response of the system (scope+generator). Since the generator has quite a well behaved step and is much faster than most scopes, the response can be interpreted as that of only the scope in most cases.
Leo's spike/impulse generator version should be directly usable for this (just take the FFT of a single impulse or average of many) without all the extra math. I'd imagine the spectra of the impulse version to be slightly less flat than that of the step version (when used as above), but I don't know if that has been tested.
With either method (step generator with d/dt, or impulse generator), you must limit the FFT to a single impulse rather than a train of them, or the FFT will be 'spiky' instead of smooth and continuous.
Aaron