I understand that the SSPX uses the 1962 missal.
Included in the 1962 missal, is the elimination of the Leonine Prayers after Mass, the elimination of the final confiteor right before communion, the elimination of the Last Gospel, and the addition of Saint Joseph to the canon of the Mass.
I feel that these are not good changes for multiple reasons.
Firstly, Pope Leo XIII added the Leonine prayers for the Conversion of Russia, and to combat the devil. Leo XIII witnessed a vision before the tabernacle. Jesus and Satan were there and He allowed the devil 100 years to destroy the Church. The elimination of these prayers is -not- helpful, in my opinion.
Secondly, the final confiteor right before communion is very necessary in this day and age, because of the corruption of customs we're experiencing right now, especially regarding women's dress. The final confiteor and the absolution at this point before communion is necessary in this time more than it ever was before since people are routinely distracted during Mass because of this problem.
Thirdly, the elimination of the Last Gospel, in these days of False Ecumenism, is such a terrible idea, because it mentions the fact in the part read after Mass, "He came unto His own and His own received Him not." I feel this elimination might have been allowed to cater to the Jews that were already interfering in the Vatican back then.
Lastly, when you're on a battlefield, you don't want to run to the front line, and draw the line in the sand there, and fight. You want to give yourself some room. What I'm trying to say is, why would you run to the front line (1962 missal) when you should be way back (1957 and before) to combat the modernist forces that wish to hybridize the 1962 missal?
Archbishop Lefevbre said that the 1962 missal was the "last line of defense." Why stand in that "last line" when you can go back further than that before those changes were made in the first place?
These are important points that I feel are worthy of great consideration. I'll add more to the discussion later.