But also a heretic who caused fracture in the body of Christ. In fact, he is known as an arch-heretic, an heresiarch.
SSPX priest are very thoroughly trained in the theology and doctrine of the Church. They also, as a group, have that specific charism of caring on the tradition of the Church as they see it was lost after Vatican II.
However they are not necessarily stricter. Clearer, more adamant, yet often more loving and understanding. Because of their deep understanding of Church doctrine and of Scripture, you will find in them a very forgiving personality and a deep, deep love of souls and concern for their salvation, in the most truest sense.
They will not dismiss your sins as mere hiccups, nor sugarcoat the truth. Many other priests in the FSSP, ICRSS, etc, are very much the same.