Barrier strips (and those plug-in connectors that use a similar screw-down lug) are DESIGNED to work with bare wire, and the manufacturers will tell you that is how they work BEST. I've had many conversations with engineers from the manufacturers over this; back when the argument was over tinning the wires or not.
These crimp-on ferrules that have recently become popular are really intended for ONE purpose; to aid in PRODUCTION wiring of machinery which uses them, and to combat "stray strand" faults.
Properly wiring with barrier strips requires CARE; care in stripping the wires to the correct exposed length, care in twisting the strands neatly, care in trimming the exposed wire so it feeds neatly into the socket without stray strands. These ferrules are designed to make it so you can just shove the wire in them, crimp them and shove them in the barrier strip; if there is a stray strand, the plastic cup
usually traps it so it is harmless.
They DO make it easier to eliminate stray strands by putting the work "right at hand", however they also introduce the possibility of NOT getting the bundle of strands directly under the screw, which is a potential for poor contact over the long term. The plugs above put the work "right at hand" as well; if you can't get THEM wired properly, you shouldn't be wiring anything.
Like any connection... the more layers there are, the more chance for material to "flow" under pressure, loosening the connection (this is why you should NEVER tin stranded wire before inserting it into one of these connectors), and the more chance for corrosion to begin its evil work. I prefer to use these connectors with bare wire, as the really smart people who invented them intended.
It is MY considered opinion that the "work equity" paid to a project in the form of doing the above wiring carefully and double-checking every connection before applying power is more than worthwhile over the long term; the satisfaction of knowing I did the job right and using the parts as intended by those who designed them is the immediate payoff.
mnem