I have seen that the gritty texture is one of the complaints in several places. It hasn't bothered me and I have not had a smoothness problem. But I could see where that might be more of a problem if spraying the paint.
Of the fillers I have tried I actually liked it the best. I've tried Famo (didn't like it but don't remember why), the Elmer's and others in tubes (can't get it out of the tube), the ones with "Real Wood" (don't like the texture, saw dust, or fibers).
I just used the current Interior only Elmer's and it is harder to get into small holes.
I do like that the one I had been using just needs a couple drops of water to reconstitute or thin.
I will have to try the Timbermate or OSMO.
Thanks,
Seth