is the apple beta program safe

You'd need to define what you mean by "safe". The Apple beta program will not load any malware onto your phone.

However, if you only have one phone, putting incomplete software onto it is foolish. It's a bad idea. Don't do it. Based on your question, I suspect you're not a developer, perhaps not even an experienced iOS user. You should not be putting beta software on your only phone.

If you have a spare phone that you can use to put the software on, there's no particular harm.

ArturMussin wrote:

It's safe till u go donwgrade

For downgrade from iOS 11 any beta u should restore using right ipsw file from apple care support

It's only way to restore without issue

Potential data loss will be

That's why the instructions tell you to back up your data first.

No, it isn't safe. Beta software is bound to have bugs. Beta testing is for finding and reporting bugs.

If you decide to do beta testing it is at your own risk and it is advised you use a separate disk, or separate computer/phone to do it, so your present OS/iOS isn't corrupted.

It's safe till u go donwgrade

For downgrade from iOS 11 any beta u should restore using right ipsw file from apple care support

It's only way to restore without issue

Potential data loss will be