I didn't notice any difference between the two, but I haven't tested them out, only used a tiny bit once. I usually don't see the solids available at my lhbs, so I just get the syrup from the local health food store (lhfs?) aka whole foods in my area.
The other issue is that I don't know if they are processed from a non gluten source. Brown rice syrup, and the dehydrated syrup solids, are processed in either in a gluten based process (using barley enzymes), or a gluten free process, using fungal enzymes.
Brown rice syrup will say if it is gluten free. For example, Lundenberg: "Lundberg Family Farms 26 May
@Amy - for our brown rice syrup, the rice is cultured with fungal enzymes NOT barley sprout enzymes so it is Gluten-Free
If I were able to get briess syrup solids, I'd get that, perhaps in a rather large bag (20-50 pounds maybe?) just so I wouldn't have to keep trying to think of things to do with those darn used Lundenberg jars.
If it's not briess, or Lundenberg, research it and find out if it is gluten free using fungal enzymes. Because otherwise, it uses barley enzymes, and the effect of that would be like us using malted barley along with brown rice to get our own conversion.