Hi Henry!
We've had our ERSA Scope for almost three years now, and I still like it. Why I chose ERSA, was because back then they were the only ones out there at the time, and I was getting a deal on a demo unit.
There have been some occasions that because of component density (they like to put caps right around the perimeters of BGA's), that I couldn't use it...but I suppose you would have the same problem with the METCAL unit as well.
The reason we bought the system is that we were building a board that had a Texas Instruments PBGA on it that they decided to obsolete. The replacement was a BGA that had a thick metal heatsink in the top that our x-ray couldn't penetrate, so it was either spend $75K for a more powerful x-ray, or get an ERSA Scope for $20K...
-Steve Gregory-