I wish I could remember the article that talked about this, but there was actually a report disclosing how many FISA requests the court shot down as being non-compliant. The percentage was actually really high. What you gotta keep in mind is that with a lot of FISA court rulings, the government presents their request, FISA either says "yes" or "no, this is unconstitutional and here's why," the government then goes back, tailors the original request to address the original ruling, brings it back and then FISA goes "sure." Anyhow, the gist of it was that FISA is actually pretty stringent, but they're as subject to constitutional jiujitsu as any other governmental entity. If it's technically legal, FISA ain't gonna be any more likely to shoot it down than any other court will.