Most online tools like Khan academy, IXL, Mobymax, etc are primarily used by schools as intervention tools (i.e., supplements to reinforce concepts or improve student test scores) and not as primary instruction for new concepts.
If your son cannot get into a classroom and just wants to do math, there's no harm in them if he is a true self starter. Khan academy uses more videos, IXL is more student directed without videos but better for hungry learners that move quicker.
I'm not sure what parent dashboards look like. Teachers can monitor progress, areas of difficulty, assign tests and extension assignments.
I loathe KA as an intervention tool, but I cannot speak to its use as a primary instruction tool. I would recommend looking up the curriculum your son's school uses (if it is standard) and finding alignment there with IXL or KA. If not, our school district uses illustrative math and both KA and IXL have a skill alignment track with IM for at home work that "can" teach new concepts.