- it's normal link re-direction / why does it happen?
It's common behavior for domain owned by certain domain service, where they perform redirect for advertising purpose.
So, it is only normal redirect for advertising purpose because SegWit address organization is no longer active like Satoshi because job is done?
It's because who used to own segwitaddress.org domain doesn't perform domain renewal, which costs some money. In addition, there's no thing such as official organization for SegWit or Bitcoin since Bitcoin supposed to be decentralized.
Should be safe, if it's a commercial purpose? Or is it harmful?
AFAIK it's not harmful since it's currently operated by GoDaddy, which is popular domain/web hosting service for >20 years.