One advantage of the mamiya TLRs for macro is the very generous bellows extension. Closest focussing distances are very close! I've found it works really well with either the 80 or 55mm lenses - but you must have a paramender. Also, it must be a GOOD paramender! The earlier model can wear a bit so the camera can droop a little and also rock from side to side. Not much, but when doing macro a tiny movement will upset the framing, so better to invest in a mint Paramender mark 2 than pick up the cheapest thing you see on eBay.
Of course, if living macro is your thing (butterflies and stuff...), forget it, the one disadvantage is that cranking the paramender up and down does kinda wreck the spontinaity and yes, the damn things always fly off. Nearly as bad as the time lag from pressing the button to the camera taking the picture on a digital ;-)
I also saw the double iris lens for sale on eBay recently. I've never used one, but they are about...