I haven't used that particular collet adaptor but I've bought several things from Joel, both original Atlas (like a 12" Tailstock Turret) and that he made (like a vertical head for the Atlas mill. I've found him to be reliable and a good machinist.
I won't comment on the price but I think that some of you are being unreasonable and/or too picky about the whole subject. He lives in the USA, not China. The only reason for using the more expensive ER-40 collets and having a 1" through hole in the chuck would be if you needed to machine a lot of short parts larger than 3/4" diameter. I don't know of any lathe with a 1-1/2"-8 spindle nose that will take more than 3/4" through the spindle. Anything larger than that would make for a fragile spindle.
He obviously can't honestly quote any runout specs because he has no control over the precision machining abilities or lack thereof of a buyer. If the buyer totally botched that job and didn't come close to the quoted specs and wanted to make the seller eat it, eBay today would gladly let him. I haven't encountered an eBay employee since about 2008 smart enough to be capable of understanding why that would be obviously unfair.