Yeah, lots to be said in favor of the boot-simple Weldon Shank tool holders. They just work.
I like the idea of ER holders from the perspective that I got very used to having access to a large tray of collets for the matched sets of Milling Tool holders we had at work, so if I wanted three different, say, 1/2 inch shanked cutters, (rougher, finish mill, ball end, for eg.) I could set up three of that size, without needing to have multiples of every size, as you would with Weldon style. That is still how I see tooling up a mill, using multiple of one ER size chuck, with multiple sets of collets in hand, so as to allow maximum flexibility in use.
I'll also add that the mill I used most, had a push button to operate the air cylinder powered drawbar (no rattle wrench, it compressed a stack of spring washers, and used a draw stud), so setting up a bunch of cutters was pretty normal, rather than just swapping the cutter in one holder.
My go-to for Large cutters, (on a 40 taper spindle) was a Nikken Lyndex hydraulic milling chuck, that held on to the cutters like they were welded in, once you torqued down the outer nut. I stalled out a 7 1/2 HP milling spindle with a large HSS end mill in it, and it did not pull out! Needed a coat hanger to recover my undies, pert-near, but the mill did OK!
There are a PILE of different entire systems of tool holders out there, stick to simple at first, buy the fancy stuff later, if it looks to offer an advantage over what you have, but only then. Unless it's a bargain! LOL!
