To dispel one thing right off the bat, I am not a priest, but I am indeed in good standing with the Church; I am a parishioner at a Diocesan parish which weekly offers the Traditional Latin Mass.
I am quite familiar with the groups I have mentioned, having met with them all on separate occasions. When I say reliable priests, I mean good and holy diocesan bishops and priests whom I personally know or who have met. The opinion I gave was really theirs, it just merely seemed to make sense to me. SJC is indeed new, founded in only 1999.
By law they are a Public Association of the Faithful (just because they add the word Diocesan to that, it DOES NOT make them Diocesan Right). Being they are only a Public Association of the Faithful, they do not yet have full legal approbation from their Ordinary nor the Holy See. Their next step would be to become Diocesan Right (a true Religious Institute, with fully binding public vows), then perhaps Pontifical Right (that is when they answer more directly to the Holy See, rather than the Ordinary).
I’ve done a lot of research on this, because I myself am interested in joining a good community one day. For the time being, I am a humble college student.
The reason I mentioned FSSP, ICRSS, and SJC together, is because I know (and know of) many people who seem to think these groups are the only valid avenues for living a traditional community life, and having access to the Traditional Latin Mass.
The spirituality of the first two I mentioned is incredibly skewed. The FSSP say their charism is simply the TLM (the Mass is NOT a community’s charism, other things are; Rule of Life, missions, apostolates, method of prayer, saintly devotion, etc). The ICRSS say the same thing, but it is worse, they have the arrogance to call themselves CANONS. The ICRSS priests are not canons. They are a Society of Apostolic Life (of Pontifical Right though), and members of a community like that CANNOT (according to the law) be canons. I have here an article explaining the absurdity of their claims.
frgabrielburke.com/2010/12/some-time-traditionalists-are-their-own.html
As for SJC, they have written out a specific spirituality, but you know what I wrote about their situation, and the opinions of their future I have transmitted here.
As for other good communities, despair not, I can name a few, of long-stnading stability from coast to coast, and even to Europe. One I can think of is St. Michael’s Abbey, of the Norbertine Order. Another is Clear Creek Abbey in the Diocese of Tulsa, OK, of the Benedictine Congregation of Solesmes (they exclusively celebrate the Old Rites). Another is Miles Christi, which celebrates both forms of the Roman Rite (they love Gregorian Chant and Latin). There are also the Canons Regular of St. Augustine in Austria, who just recently made a new foundation here in the United States.
I could well think of many more. I just want young aspiring men to realize that there is an avenue for their vocation in other good places; places which have a genuine, good spirituality, a tradition (by that I mean traditions developed over time by the community’s age), and are in tune with the patrimony of the Latin Church. I hope I have been of some help explaining myself. I’d be happy to answer anything else. Merry Christmas!