I haven't heard of it and would now not consider getting it for my kids. Why would I bdavka go against the roshei yeshiva?
The same reason I vote against anyone the VAAD endorses.
What message does it send to send to your kids if they are aware of the Kol Kore (hearing from classmates, shul, etc) and yet (perhaps for a legit and 'justified' reason) you sign them up for this app/device?
People and Rabbanim can have different opinions. I think this is something that is missing in today's chinuch. This part of the discussion is moot because my oldest just turned 6.
I'm more concerned with leaving my kids watching the alternatives. Until recently there was only non-Jewish content available (nickelodeon, PBS Kids, Sesame Street, etc.) which was fine when we were growing up, but nowadays a lot of it has woke garbage mixed in. I recently signed up for toveedo.com which is a Jewish alternative (also without any haskamos), but I'd much rather have something that isn't Lubavitch. (No, I'm not looking to have a public discussion about why I'm not thrilled with a Lubavitch option).