Micro Seiki ma-505 x is a low or heavy tonarm?

 Here is a discussion about that arm. The head shell weighs 9.7 grams!    https://www.vinylengine.com/turntable_forum/viewtopic.php?t=48848

I own a Micro Seiki DD 40 with dual tone arms Both MA505. One has the Ortofon Black and the other has the Denon DL 103R. My question is as long as you are able to balance the tonearm is the tonearm mass a non factor. Thanks

No. Tonearm effective mass and cartridge compliance determine the resonant frequency of the ensemble. Has nothing to do with balancing except insofar as the counterweight and its distance from the pivot do affect the effective mass.

The MA-505 series is a dynamically balanced tonearm. It reacts completely differently than a statically balanced arm for tracking purposes. The mass is 14.5g (with the standard Micro Seiki headshell) and it was designed primarily to work with all cartridges, but especially with very high compliance cartridges which were all the rage when this tonearm was designed. But it works great with moderately low compliance or heavy cartridges. It's one of my favorite "budget" tonearms.