A lot of people use toner transfer to make a resist for etching.
I guess you’re talking about just using the toner as a finished graphic itself? Seems fine, if you like the way it looks
I’d definitely put some kind of clear coat (might have to experiment a bit to see what works) over it. Otherwise I see it flaking off pretty quickly with use/handling.
Sealing it without melting/dissolving it is the kicker.
Also, getting a clean transfer isn't 100% guaranteed. It's without a doubt the hardest part of etching enclosures.