The latest vid wasn't as cringe worthy as the others and somewhat informative but I'm left still wondering if this is a good money sink for us or not on our trip (we get in at around 7pm and my son wants to go to MK After Hours SO badly, but for us 2 it's $300!!!). I didn't come away with any real opinion on it, I don't think he sold it terribly well.
I am not a professional Disney vlogger, but here's my two cents. First, I think the vibe of the HS After Hours is going to be VERY different than the MK After Hours. The MK After Hours will be more crowded. I really don't think you can or should compare the two.
What is the reason your son wants to do the MK event so badly? Short wait times? Night time experience? Special characters? Just something to do the night you get in? I think his reasoning would ultimately determine whether the MK event is worth it for your family specifically.
Honestly, if just riding rides is the reasoning, I think plunking down the money for Genie + for the day would make a full MK day more worthwhile and it would be much cheaper. Pay attention to park hours, make your MK day the day where it is open the latest. The wait times for rides get much shorter as the night gets later.
If you happen to be staying at a WDW deluxe resort, I will say that the Deluxe Extended Hours event is 1000% worth it. It's included in your stay, only available to Deluxe guests for certain night at MK and Epcot and is truly an empty park experience.