How cold depends on how it is set. Many, but not all, are adjustable that way. How fast it gets cold is pretty slow. Mine works well, is set to cool to around 35 in the fridge, but it takes it 6 to 8 hours to do that. Once it gets down there, it'll stay there (and has, for months, no problem). None of the absorption-type refrigerators cool off really fast.
That said, I have also noticed no particular difference in either the speed of cooling or the ultimate temperature between 120 v electricity and propane. I usually keep mine set on auto-switchover, and leave it running on propane while towing, and it cuts itself over to electric when I get shore power.