The Still River people generally are much more sensible and Orthodox than Br. Francis and his various sattelite groups. I very much like the Benedictine group at Still River, who I think most closely follow where Fr. Feeney and Sister Catherine ultimately ended up. Needless to say, I used to go to Mass there when I lived in Acton and Lowell when I didn't feel like going down to Holy Trinity (which was officially my parish).
The major doctrinal distinction when dealing with the Still River folks is that they place various modern theories of Baptism of Desire in question, most especially the notions of implicit Baptism of Desire and implicit Faith - fine with me, I don't accept "implicit faith" either, as there is nothing in the Fathers of the Church or its Magisterium to support these extreme theories of Karl Rahner and the rest of the Modernists. Much of the crowd around Br. Francis, however, openly questions Baptism of Blood and and either revile or lie about St. Thomas Aquinas and other medieval doctors for holding both it and Baptism of the Holy Spirit (Baptism of Desire in the strict and explicit sense, as defined at Trent). Worse, they misrepresent the teaching of the Church and twist it away from its proper meaning to support their heresy. That is against the Church, and these are the people who rightly or wrongly are properly tagged Feeneyites.
Its worth pointing out in this regard, the definitions of Trent and the works of the medieval Doctors used the word "votum" to describe the relation of the unbaptized man who could be saved towards Baptism, not "desiderium". "... sine lavacro regenerationis aut eius voto ..." - "except through the laver of regeneration, or a desire for it" (Trent, Session 5, Chapter 4, Dz. 796). "Votum" means literally "a solemn vow to God", i.e. the resolution a Catechumen has to receive Baptism once he becomes convinced of the faith, and identical to the resolution of any Baptised person to have recourse to the sacrament of Penance when it is unavailable because of some dire circumstance ("reconciliationem ipsi contritioni sine sacramenti voto, quod in illa includitur, non esse adscribendam" - "this reconciliation nevertheless must not be ascribed to the contrition itself without the desire of the sacrament which is included in it"). "Desiderium" means "desire", "longing", or "yearning". That is the word whose sense gets appended nowadays to "votum", although it clearly should not be.
I've always found the most remarkable thing about Fr. Feeney is that God used him as his trumpet throughout the earth. When I was in darkest India, the controversy over "No salvation outside the Church" and Fr. Feeney was alive and well and paining the Hindus.
I read they were not "regular" on a website run by the Mission Church (Basilica of Our Lady of Perpetual Help) in Roxbury -- I think it is run by Redemptorists. I thought the Mission Church was wrong in its characterization of the Still River people. I'll drop them a polite line and ask for them to remove the codicil they have attached.
I don't know much about Fr. Feeney but I remember my dad telling me (my family met & knew Fr. Feeney slightly) that the situation was so volatile that Cardinal (maybe bishop at the time) Cushing went off to Rome to have the pope intervene. I guess that would have been Pius XII? And Fr. Feeney was therefore chastened.
I also occasionally attend the Tridentine at Trinity. Are you still a "bay stater?"