The 50 parishioners per chapel was a very conservative estimate. I have been to a chapel with 30 people at the only Mass of the Day and one with over a 100 at Mass, then there are some with huge amounts of parishioners like the one you go to and others that are very small. I think maybe 200 would be a better average of parishioners, so at 115 chapels in the US that would be 23,000 people just in the sspx. Then in Europe and elsewhere especially France it would make the amount of sspxers into the hundreds of thousands. And then add in everyone else and it isn't that tiny.
I guess you could say it is an anti-Jєω extremist group, it is called Roman Catholicism. It is extreme, it is extremely different from the hedonism and paganism of the modern world, and it is anti-Jєω, and anti-any other religion as we believe that our religion is the one true Faith and all other religions or offshoots are heretical so naturally we are anti-judiasm (and all other faiths).