My experience is dated, back when they were only 3 cuft, but I had some extra cash and picked one up. Before the SA, I never carried redundant air, I used the surface as I was trained. Since I was trained before SPGs were widely used, and not all tanks had j-valves, and sometimes the j-valve was knocked out of position or forgot, I did a lot of CSEAs and it was no big deal. The normal and maximum ascent rate was 60'/min at the time so it was faster than the normal 30fpm used now, although I believe the maximum rate is still 60fpm.
The SA worked quite well to assist in a CSEA, however in the environment I dove, the regulator regularly got crap in it making its operation unreliable for me, and increasing maintainance. If I was a boat diver at the time that problem wouldn't have arisen.
Since it was inconvenient, I quit using on it on dives, and years later sold it. I went back to using the surface as redundancy when doing recreational dives. As I got older I do now use a pony for deep dives, but the ocean shore dives aren't deep. I would have the same problem with the pony, but a normal second stage is more robust than the SA, and with a bigger bottle one has more air to waste on a slow leak or free flow.
If one panics when they run out of air, a SA won't help, but a pony may not either. For a diver that has a plan, then it's a matter of deciding on how much air they are comfortable with using to assist with a CSEA, or making a normal ascent with air to spare for all contingencies.
Personally it is the divers choice, not mine, and it makes no difference to me if the choose a 3 cuft SA, an Al 80, or the surface. The crux of the issue is whether the diver practices whatever method they choose, and is confident of their ability to successfully follow that training.