Is SPF 100 significantly better than SPF 50?

No, it’s not significantly better. SPF 50 blocks about 98% of UVB rays, while SPF 100 blocks about 99%, so the extra 1% doesn’t translate to meaningfully better protection in real-world use. The real problem is that SPF 100 makes people skip reapplying or stay out longer, which is dangerous. You’re better off with SPF 50 that you reapply every two hours.