Mark, I do 95% of my turning with replaceable tip tools on a Bantam, and I have a knife tool with triangular tips, and also a large boring bar using the same tip. I have a chamfering/facing tool using square tips, a small boring bar with small triangular tips, I use the same small tip on a fly cutter on the mill. I have a JB 6mm round button tool for nice radiuses when I need them, and a JB diamond shaped tool to use with a live centre, and a JB tipped parting tool which I use in the rear tool post, and that is it.
The tip holders are all branded, and all use ISO standard tips which are available everywhere. I have never ever had a problem with the Torx screws, but I always blow any dirt or swarf out of the screw head when I change them.
I would always go for used branded tool holders over cheap new ones with non standard tips. I would not buy sets just buy what you need, and check the on line catalogues for extra information.
Chris Gunn