Reading spoilers for series like 'My Hero Academia' can be a real gamble. From what I've gathered, Readmha seems to be a fan-run aggregate site, not an official source. The safety question is two-fold: virus/malware and accuracy. I haven't personally had issues with redirects there, but I use a robust ad-blocker, which I'd consider essential for any site of that nature.
The bigger risk, honestly, is trusting the spoilers themselves. They often source from leaked raw scans or early translations, which can be wrong or miss crucial context. I got burned once believing a major character death that never happened, and it really colored my reading of the actual chapter. For safe spoilers, I'd still lean toward moderated communities on Reddit where users dissect and verify leaks, rather than a standalone site that just posts them.
Even if it's technically safe to visit, I'm not sure it enhances the experience.