I think overhead joins are fab (second only to the RIAB), especially where non radio traffic is involved or if you are sorting out an approach to a scary new field.
But one thing I must add. When is the CAA going to come up with a readable version of the OH join pattern. The coloured fields add loads of 'colour' but you can't read the words without a magnifying glass and (Rabbs you are right to ask) the poster does not make it clear but you CAN make an OH join from ANY direction - thats the idea.