why a custom built converter isn't for everyone....

In what respects? ET? How it drives? Both? Neither?

Making a decision as you first asked is largely based on what your expectations (optimization, potential etc) are and how you define them.
yes, to all of it when speaking of Max Performance. But my point has been, when building "dirt road budget build" vehicle, and parts or being thrown at it and continued to be thrown at it, a custom converter isn't optimal for the budget because the changes would be enough to warrant "another custom" converter.