Here he is on some 19th century priest dude who didn’t pan out well.
I don’t know if this analogy is really helpful to… I mean, a lot of Lammenais’s ideas were actually pretty good ones, although admittedly he took them to unfortunate extremes. At the time they seemed radical, but today most of them are widely accepted. The first of the two encyclicals that addressed Lammenaisism, Mirari Vos, was for a long time the archetypical cudgel used by anti-Catholic bigots to bash the Catholic Church (in America; I don’t know if other countries had the same reaction). Singulari Nos never attained quite the same notoriety, but I doubt it would have been popular. (I just googled it, and apparently Singulari Nos did feature prominently in one anti-Catholic pamphlet, but that pamphlet just flat-out lied about what it said)
Admittedly, while his ideas may have been good, that doesn’t mean his actions were.