I've only ever seen alt trigger on a few cheaper scopes - not really sure why you'd want it - I suppose there might be some rare situations where you need to see the shape of 2 unrelated signals simultaneously.
Are you kidding?
Simplest possible example from yesterday. I want compare two separate signal generator waveforms. Both generators have its own clock. (they are not sync with each other but I want look and compare signal shapes conformity with several different settings. Without ALT trig I waste lot of time and time is money.)
Gen 1 to CH1 and Gen 2 to CH2 and compare wafeforms shape, scope to ALT mode. Set CH1 and 2 triggers and go...
How you do it without ALT trig. And this was just as simplest possible example.
ALT trig have been normal feature in oscilloscopes as long as I remember.
And this is not enough, there is also ALT trig with real dual timebase. (in history and today but these are not usual in entry level cheap scopes)
In analog scopes specially it is very normal feature in all professional analog scopes (I do not remember any scope what do not have it).
And even more, one Tektronix have real dual beam (not only dual trace) expensive model what have real dual independent beam in same CRT.
There is many situations where is useul to look two signals what are not sychronized and not only dual trace...
I think if there is not ALT mode it is just exeption.
If there is ALT trig with dual timebase this is littlebit more rare but also nice useful feature in many lab work.
But of course I have only around 40 years experience with lab work and field diagnose in industrial world where need repair and adjust things and becouse this it is possible that I do not know enough for claim that ALT trig is is in class "not useful"
But also, I have seen sometimes peoples have done bad mistakes with ALT trig.
My Tektronix 7000 have it and more, also Tek 465 have it, Tek 2200 serias have it and Tek2400 serias have it. Do you think they do this feature just for nothing. If professionals do not need it they really do not make it.
It is real shame if this Agilent model do not have it.