Hello Raul, I'm mostly an accidental tourist with respect to tonearms, having owned only around 12 over the years. Of late I have gravitated to the SME 3012R and compared this to a 11" Kuzma 4Point and a Micro Seiki 808X on the same turntable. The 3012R and the 4Point have identical 14gm effective mass. The SME is arguably the best of the lot, and does great with both high and low compliance cartridges. Maybe SME got it just right with the stainless steel wand. I've heard that the R was more popular with Japanese audiophiles than the other versions, and to some surpasses even the IV and V. The R delivers possibly the best neutrality and LF delineation I've heard. Not the biggest bass, but perhaps the most well controlled and natural.
I don't understand why setting up a 12" arm should be more difficult than a shorter arm. I've been careful to find precise pivot-to-spindle distance and use standard null points on a db protractor.
Regards,
Dave