I picked FAST ez2.0 because it would run on e85.
I ran it for a year then switched back to gas when I went on Power Tour in 2016,have not gone back. Car ran great on e85,I had no problems at all.
The only “problem” came from the FAST system it self,the self tuning requires you to “go” to the “cells” to tune them.That takes some time,and caution. You have to push it into the ranges that are not happy,several times.
Push it into unhappy,then down,repeat,go a little higher,repeat. Over and over
A separate fuel mixture indicator comes in handy.
It would drive me nuts though because it was always tuning.
I purchased an e85 tester and learned why,tank to tank the blend was never the same.seemed like it anyway. Here in TX. Jun Jul,Aug dead on 85% from my local station,the rest of the year....lowest percent was 60%. In Jan,early Feb.
Go out for some fun and the high rpm tune was suddenly not happy. I never felt it went lean,but 5-6:1 was normal when not happy.
Never had any of the horror story problems though.