Hi
As post-2 says, the cascode extends frequency response by shielding the lower Q from the load, keeping the collector voltage for the lower Q nearly constant so it has effectively wider bandwidth. The output impedance of the upper Q is quite high and it needs a light load to provide maximum bandwidth and signal swing.
Bootstrapping the load on the cascode helps maintain the cascode bandwidth and requires that the upper collector is buffered from the bootstrap point and load.
The "active" load is just a current source, which is a standard feature in amplifier voltage gain stages. As the name implies, it keeps the current through the circuit constant and is the same effect as bootstrapping but without some of the turn-on problems a bootstrap might introduce. A benefit of the current source is that the circuit has full performance right from a very low supply voltage up to the full design value.
In a CRT, there is a need for fast-rising voltage steps and to handle high-frequencies, so anything that reduces the need for high-value compensation caps is good: cascoding, current-sources, bootstrapping.
Note that all current sources are not made equally. The 2-BJT type with local feedback has wider bandwidth than the simple buffered voltage references. The speed can be improved if you add a small base-stop to the current-sense BJT, then add a small cap from its base to the collector of the pass element of the current source. 15pF is typical. The current source can also be cascoded.
I think you would look at it as adding the current source is the best first step to improve the circuit, then add the cascode as the next step UNLESS the circuit already has an EF buffered output with a bootstrapped base resistor, then add the cascode first.