I shot a .22/20 ga version. My problem was that there had been no apparent effort to regulate the barrels, so there was no way to figure out a sight setting that could be used for a 20 ga slug and the rifle barrel. For a rabbit/squirrel gun with the shotgun barrel loaded with shot it will work fine, and that is what it was designed to do.
^this
IIRC the bottom barrel is just floated in a steel collar soldered to the upper barrel (or vice-versa, its been awhile). its not regulated at all.
i had one in .223 and 12 gauge, what at the time i thought was the most useful 'all round' combo. if i sighted in the irons for the .223 - or a reflex sight mounted on a rail on the receiver - then a slug loaded in the 12 gauge barrel was several feet off.
IMO what it excels at is this:
if you sight it in for the rifle barrel, its actually reasonably accurate despite the thin rifle barrel with the heavy weight hanging off it. if youre hunting coyotes for example, and have it scoped, its accurate enough for 200yd shots.
if a coyote comes in close, you see some grouse, rabbit, whatever its easy to switch to the shot barrel which is accurate enough at close ranges.
in retrospect, i should have got a .22LR/20 gauge instead of the .223/12. i find that the extraction on the Savage 24 is way too weak for centerfire - i was having serious problems with the .223 extraction and just didnt trust the gun (why i sold it). i also noticed the telltale signs of extraction issues on other centerfire 24s i examined (signs of prying with a screwdriver or knife between the barrel and extractor).
one upgrade that helps - and im going by memory here - is there is a pin at the front of the receiver (perpendicular to the bore) that when the action is opened, actuates a rod that pushes the extractor. this pin is some soft mild steel and over time, and with more 'stuck' cases, will actually bow into a slight curve shape -- which even
further weakens extraction. IIRC i replaced this pin with one i fabricated from the shank of an HSS drill bit and extraction improved dramatically.