There are two camps who are using the old letters. Those who think the letters and fun and different and maybe we lost something when we stopped using them.
And then there are those who might be using them as a dog whistle of sorts. The darker side of the "we lost something" sentiment. Y'know; "Make English great again" but with exclusionism and jackboots. (See also: Anglish, which has the same problem.)
I'd quite like to be one of the wacky bunch who uses those letters occasionally because they're neat, but I don't want to be mistaken for the other sort of person.
There's also a problem with old letters anyway. "The" was spelt with "þ", not "ð" despite the latter having the correct sound, and so you'll see people altering the spelling of "þe" to be "ðe". This iz equivalent to spelling sertain other wordz with the wrong letterz. This annoys purists of all stripes, jackboots or otherwise. (Heck, I'm not even sure which is the right one for "other". "th" covers all bases.)
I mean, it's almost worth it to annoy the fascists, but it's probably best just to leave the old letters in the past.