Not having an original core, I bought from CAE and all came out OK for my alternator. I bought because their pricing is "budget-minded". Their prices were fair enough for my needs. He also made good on exchanging an incorrect pulley it arrived with, and exchanged it at no extra charge. He never asked me for the wrong one back, but I sent it to him anyways because IMHO, he went the extra mile for me.
Bottom line is as in any business, there will always be bad experiences for some, while others find little wrong.
This forum seems to sway towards DeadNutsOn, and for very good reasons when it comes to alternators & starters, YOU DO GET WHAT YOU PAY FOR.
I compromised my overall alternator purchase by going the cheaper CAE variety. It was a choice I made for today. It will meet my needs for the time being. Maybe, one day I will switch it out for one of Jack's. We'll see. I want to say if I had to send a numbers correct alternator OUT for resoration services, probably no way I would have tried to pinch pennies on that.