Threaded cutters are now a special item out here. The reps I deal with do not stock any threaded cutters now. Only 1 supplier that I know of has them and they are more expensive than a coated solid carbide cutter up to 10mm diameter. With the clarkson, I used to have a set of threaded ends to make the collets be able to hold non threaded cutters. Never had one come loose or let go. But now they have a full set of R8 collets, so just use those instead most of the time. The Clarkson is handy when you are drilling some holes or change back to milling, the the table or head height does not have to be adjusted so much.
The ER series work well, but the tool really needs to have 90% or better length location into the ER collet, or else they have a tendency to clamp harder on the back of the item and in turn leads to the cutter walking out of the collet.
For the smaller diameter cutters, I like to use the smaller collet series. As for the sale price on an AutoLock setup, the 2nd hand market for them is a joke. Especially when you consider the quality of the AutoLock unit and how well made they are and what their new price as the time. But that must be a sign of the times I guess. I have an Autolock, but won't ever sell it. For the odd time that I do use it, is worth the shelf space.
Neil