Yes, I tried it... once.
I was down to my last sprays of Prothik and I too thought that "since it(Fullmore) was made by the same people who made Toppik" that it should be pretty good, because I used Toppik and was always happy with it. So I decided to give it a try. That was a mistake. If you don't want the "painted scalp" look, stay away from Fullmore. Because that is all it did, paint my scalp. It didn't even attempt to adhere to the hair that I had left.
Still used Toppik fibers, with some more Prothik(although by this time they themselves had changed their formula and bottles and I was growing unhappy with them for those various reasons) after that. But never touched the Fullmore again.