I haven't used any online options for my own kids (other than online college/dual enrollment courses, which would be a different conversation), but my experience with students transitioning into our secondary school after a year or more of using Connections Academy has been that they have been not noticeably different from b&m-schooled peers in the ability to fit into academic programming. I haven't seen enough students from other online schools to comment on them.

...pronounced like the long vowel and first letter of the alphabet...