Father Schreiber is an exceptionally friendly, down-to-earth, and, of course, devout priest. He is undoubtedly well-suited for the office of auxiliary bishop.
However, one will not find in him a lionhearted fighter like Msgr. Williamson or a "theorist" like Msgr. Tissier.
One should not expect a great leader in the fight against modernism, but certainly a thoroughly traditional bishop who not only preaches the faith but, first and foremost, lives it himself. 
The German-language YouTube channel of the SSPX offers numerous videos (sermons) by him. Naturally, they are in German.
Piusfilm (German SSPX YouTube)
To not fight against modernism is a grave sin of omission for a priest.
This is the main reason we should avoid the SSPX at all costs for Sacraments.
I would have more faith the sedes had they not all sketchy Sacraments.