Grinner ---- Uniknot are they knot the same thing?
Yes and they're both the same as the "nail knot" when pulled up.
try tying them in the thickest line you can manage (clothes line or some cord) and see that when they're neatly finished they have the same shape.
The only advantage of a grinner over a uni is that the initial turns (which come out of the knot as it is tightened up) help guide the wraps as they "capsize" to more easily snug down neatly without any crossed-coils.
PS there is a knot called the "Stren knot" which consists of a uni in the mono but a half-blood knot in the braid and is supposed to be stronger than a uni-uni when joining braid to mono.
I think there is supposed to be less tendency of the braid to cut the mono when under heavy strain.
PPS I wonder if MIke or Mike junior should post a "sticky" on using search for (for example) this specific subject ?