I have an old Pentax 6x7 which made lots of money for my studio "back when" by doing copy work with the 135 macro. For most of that work, no additional accessories were needed. Eventually I had to buy the tube set but never needed any more than a single tube from the three tube set. The bellows were never under consideration due to their cost. Long after my career was no longer in the studio, I did acquire the bellows, dual cable release, etc. My opinion: it is a royal pain in the ass (no insult intended, feral donkey) to use and is of no practical-world advantage over the tubes unless you consistently do larger than 2:1 macro. Of course, your mileage may vary.

Russ