Strangely enough...
I repaired one of these Brush things the other day, it was a BaByliss brand and cost £50 I'm told.
Really poor quality inside and looked like the ones in the video! I was surprised when I was repairing it at how dodgy it looked inside and
wanted to bin it rather than repair it, they have 2x DC motors inside and have really crude rectification and voltage dropping, the one DC motor had sized so ran it up on the bench PSU for a bit with a few amps up it (This is the one that turns the brush) I think she must have jammed it at some point and the brushes had stuck.
As long as the "transformerless", solution is safely inside a case, and doesn't present any kind of safety risk, externally (e.g. unlike some unsafe/dodgy USB chargers, as shown by some of BigCliveDotComs videos). Then, it is NOT too bad.
It is when a beginner/low-end-hobbyist, messes around with these, potentially (excuse the pun) highly dangerous circuits, that people get concerned.
In fairness, it is NOT limited to electronics.
Potentially unsafe youtube videos, can be found, in all sorts of areas. Unlike, in the "old" days, of when things like that would only be usually seen on TV. With the TV company, using "professionals", to ensure that the TV programme, would only show "safe" things and supply any safety warnings as necessary.
These days, youtube videos, can show all sorts of, crazy/unsafe things.
E.g. Youths (seemingly, often Russian), climbing up, apparently hundreds of Metres, WITHOUT any apparent safety equipment, such as safety harnesses.
Then at the top of buildings, precariously, climbing round the top of the building, while only holding on to some dodgy part of it, with one hand.
Such videos, tend to make me sick and/or look away, when I've seen them.
Example: