I have some notes in my build thread on the KYB Monomax shocks.
I felt a definite improvement in my ride quality with the new shocks, particularly with full load- I rarely drive the truck for anything other than trips and very inclement weather.
As others have said installation can be slightly tedious but should be doable by anyone with a pair of working hands, two nuts/bolts on each and you're done (generally speaking).
I did fairly extensive research on their comparison to Old Man Emu and Iron Man in particular. I'll let you guys do the same homework I did (or look in my build thread, I mentioned some specs if I recall correctly) but my conclusion is that A) they are made in Japan. B) They are (or were slightly more than) equal in dimensional specs of the OME and larger/heavier duty than Iron Man. This translates to their strength and ability to dissipate heat. Both good things. C) KYB Monomax was significantly less expensive.
My truck has OME Expedition heavy rear springs and Iron Man torsion bars fitted.
I have not driven or ridden in a comparably equipped Montero with OME suspension, but have driven a plethora of rigs with OME suspensions. I can only speak of the improvements the shocks made on my truck after switching from the adjustable shocks. Two thumbs up.
Upon arrival, I noticed the welds, fit and finish, were on par with OME. I attribute that to the Japanese manufacturing.
I'll also be equipping my FJ62 Land Couch with KYB Monomax shocks.