The "Sweet Child O Mine" riff did it for me.
I can't comment on how close it is to a Marshall JCM800, as I don't own one to be intimately familiar with all its tones...but you gotta consider that all these amps have a lot of knobs, and moving 1-2 of them just a little, usually changes things noticeably.
IOW...can only a Marshall JCM800 do that tone, and is there only one tone that it can do?
I know the answer is no...and I'm not looking to offend any Marshall fans at all...just saying that even 10 vintage Marshal JCM800 amps don't all sound the same.
AFA the sound of the Ceriatone 2202...and the 6V6 tubes...yeah, there's a difference between them and EL34 tubes, though I always considered the 6V6 to be like the kid brother of the EL34 tube. They both have a bit of that "squish" in the low-mids, with the 6V6 showing a bit more growl, while the EL34 a bit more punch. That said...the tones in the videos are pretty good...but again, you can probably find a lot more with twist of the knobs.
I lieu of an EL34 amp...I would rather use a 6V6 amp that's trying to do the crunch thing instead of an EL84 amp, which IMO sucks at it, and I've never been able to get comfortable with EL84 amps doing fat crunch/distortion tones. There's always something fizzy about them....they're better off doing the Vox-ish chimey thing, IMO...and I've had, and sold every EL84 amp sooner than later. I don't have any more, and will probably never buy another one.
My current roster is EL34 and 6V6 amps...though I have to say, that last year when I got my fist Carol-Ann (the OD2r)...I was amazed at how much I liked the 6L6 sound of the amp. I'm really liking the clarity and the crunch, plus the low end is like super fucking tight.