Before this shoe, I ran in the NB minimus zero for 6-7 months, which is more similar to a racing flat. Although running ultras is doable in the NB M0, the Altra is a much more comfortable shoe for long runs. Where as the NB minimus is like a Porsche GT3, the Altra is the Panamera. Bottom line - this is still my favorite "minimal shoe" and would give it 5 stars if the sole was more flexible.
This review was written in the old system and had content requirements that are different than reviews written today.