I’m also a former Geodisc user and a current Feickert user. The Geodisc sort of worked, Sighting the pivot point along the ridge was always problematic, and with some arms extremely difficult. I used it in conjunction with a DB Systems protractor for the final adjustments. I’ve also used other methods in the past.
The Feickert is simply easier, faster and more accurate than anything else I’ve used before. So far I’ve used it on VPI 10 and 12" arms, a Magnepan Unitrac (which was super difficult to use with the geodisc), and a Rega RB300 on a Denon table.