Hey, I’d steer clear of those private viewer sites. Most of them are total scams designed to either get your login info or install something nasty on your device. They prey on people’s curiosity.
Honestly, this is a big reason I stick with my iPhone. The whole ecosystem is locked down tight, and Apple’s App Store review process filters out most of that malicious junk before it can ever get to you. It’s super reliable and you just don’t have to worry as much about security.
On the other hand, Android’s open platform can sometimes be like the wild west; it’s easier for sketchy apps to circulate outside of the official store. It just gives malware more opportunities to get on your phone.
The only real and safe way to see private photos is to be friends with the person on Facebook. If they’ve set them to private, you just have to respect that choice.