I do. It does take a few minutes to "disperse" the clumps formed by trickling it in. But on the plus side for me at least it seems to have a pretty good residual quality. As you can probably imagine I tumble a heck of a lot of brass. Unless the brass is particularly dirty - in which case I'll dump in an extra ounce or so - I usually don't add more until I have tumbled several thousand cases, or my normal tumbling time (2-4 hours) does not result in "like new gold" appearance.
With this said . . . I like SB's suggestion. As I understand Nu-Finish is 100% synthetic so I can't see how a little mineral spirits could actually harm the chemical and if it makes it disperse faster . . . sounds like a win/win to me.