Connected can be so variable. A whisker thin join would pass a boundary scan and fail a few months later.
I'm quietly hoping someone buys one of these cheap x-rays and posts some honest feedback.
The full-scale images on their
example page look great. The best ones are somewhat better than what I can get out of the Faxitron.
Just to show what is achievable at lower voltages,
this message has some photos of a BeagleBone Black PCB taken with my 35 kVp (uh, well, OK, 37 kVp) MX-20. Lots of other good examples from Fraser and other people in that thread. As you can see, sub-50 kVp voltages are useful for basic PCB inspection as long as you have a microfocus tube paired with a good sensor. If you don't have those things, more voltage won't help.
This is a 6-layer board, and I have had good results with 8 layers of 1-oz copper as well. 10+ layers is probably pushing it. You may not be able to shoot through a whole cell phone, but that is debatably useful in a board-level inspection context.
If you are only interested in BGA inspection, an X-ray machine isn't really the best tool for that job. It is much better than nothing, but what you really want is an optical fiber scope similar to
this one. If you are lucky enough to be equipped with both X-ray and fiber, there's not much you can't inspect.