As I pointed out earlier, I don't care for the language that they use and their publication of "price lists" as if it were a menu at a restaurant.
Apart from that, unless you are one of the few who are able to be in contact with a priest who has availability, when you send a stipend to the SSPX for Masses, they farm them out to individuals who may or may not even be valid priests.
I know also from individuals who have told me personally that there's an inordinate delay in the SSPX making good on these Mass intentions. They take the money right away but then can take over a year to "make good" on them, and that's only if you keep pestering them about it.