If you are running with the annular discharge, I guess you have opted for this because you have a reasonably radical cam with the associated weak vacuum signal. If so the guy could be right. I found that the biggest improvement was by getting the right balance in the restrictors and bleeds and that jet change had nowhere near the effect these did in geyying a reasonable mixture throughotb the range. If its any help, I ended up with.076 on the idle air bleeds and .032 on the restrictors. The high speed bleeds needed changing, but these were done on the rig by the expert.
The result is that on a motown 415 with a Crower level 4 cam, it idles at 800 and goes like stink. Stick with it, its an awesome carb when you sort it out. I agree though its a pity that the customer relations is crap and the assembly by the sounds of it. Must admit, I checked mine as I had heard similar stories - must be lucky as it was clean.
All the best with it.
Mike