Any issues with upgrading Imac with external boot SSD and High Sierra

Hello

I am somewhat confused by what I am reading about High Sierra's issues with spinning hard drives and older iMacs.. I have a 2013 Imac which is booting from an external 512gb SSD (it was too slow with its internal hard drive). I still use the internal drive for some slower storage.

Can I upgrade to High Sierra without issues?

Thanks

Ted