Just my experience but I did what your thinking about doing and bought a socketed ECU from Z1 and then sent them my core. If I remember correctly it took them over a month to refund my core charge. Every time I called about it they said they would do it this weekend and the weekend would come and I would follow up and they would say they didn't have time and then not enough cores to make it worth there time to test just mine. I dont mind waiting but when a business says there going to do something doesn't and doesnt follow up thats when it becomes an issue. I did finally get my core charge refunded after I threatened to file a fraud claim with my credit card company.
Yes my core was good and this was the same order they shipped me a boost controller box with out the boost controller. Just wanted to let you know. Cheers