I have used them many times, both with small fish and with inverts needing larger zooplankton. However, I would only use them if you either have such an invert or a fish that is refusing food such that it's getting desperate. Last thing you want is to have a fish that is trained to pellet and suddenly decides it's back to only wanting live food again because it gets a taste for wiggly brine.
Regarding the nutritional value, it is important to feed them! It's much like crickets being fed to lizards in that regard. This also keeps them longer at room temp. Mine have gone for a couple weeks that way; never heard of refrigerating them. Brine shrimp like a few drops daily or every other day (depending on water volume of course) of prepared phyto mixes like Kent Phytoplex. I usually add a little bit of Kent Microvert too because I'm never too sure on the maximum particle size they're interested in.