The Royal Compound is a little "creamier", and so I don't experience the powder - like residue that I sometimes saw with Rough Buff. For those who have spinners without water supply,  the Royal Compound should be easier to use.  End result should be pretty close with either one in my estimation.

for practical matters, I saw virtually zero difference between them when I applied them to a ball.

I agree, Rough Buff I think had a slight gritter feel to it than royal (But that might be different batch to batch).

But in use I saw no practical difference between the two.