They are fully canonical.
They have a bit more… flair than the FSSP does. They are very Renaissance-y. I hear that they love the Baroque, but then so do I. Their Chicago church is being remodeled extensively to fit this style. They have a special choir dress, very easily identified. The priests and oblates (men who help the priests and who are members of the ICKSP, more properly the ICRSS, and can also be deacons/subdeacons) wear black choir dress which has blue piping with white rochet. The Superiors wear the same thing but in all blue, and I think their piping is white. Everyone wears this medal on a blue and white ribbon, but I’m not sure what medal it is.
I would say that, overall, the difference between the FSSP and the ICRSS is that the ICRSS tends to be pickier. I would mostly liken the FSSP to a sort of mission EF group. They are not afraid to go into dioceses that will only give them small and/or ugly churches. Now, they do dress them up, but they still look modest. That is not to say, however, that the FSSP does not have some extremely beautiful churches in their own right. They do. However, IMO, all of the ICRSS churches after renovation are absolute jewels. The ICRSS’s attitude seems to be “all or nothing.”
