I have been using these letters since i was at high school, say early 1970s. I tried out ð too, but Modern english represents both of these by a single letter 'th'. One has ick and in, weaer or neier. It's in alphabets already, there's no need for a new rune when its been with us years. Writing "ðe" for "e" is like writing "as" as "az", and other 'newspeak' idioms.
Writing orn is pretty easy, and you get to learn to keep the ascenders on p quite short. Other than that, one gets people who get confused with is. I had a comment or three to the effect that "all of my ths come out like 'p's". I usually respond along the lines of trying to enquire about whether they were Non-English-Speaking Background or something.
The letter has existed for quite some time. A recent tome in the post 'archelogical papers', bought for yet another OE thing that most folk have long forgotten (the long hundred = counts by 120), has a church registery, with the likes of 'Richard, ye son of Peter and Mary', where ye is a form of e the capital looks something like an I, with a rod coming from the middle to 1 o'clock.
The 'polygloss as nature intended' on my website, is constructed in thorns, it's quite an 'easy read', and does not look too ugly. There are some 'th' in there, because some words have a separate t and h, eg the name Wythoff, which is Wyt (white) + hoff (yard). A simple s/th// does not work. The two polygloss pages are based on the same code, made up in a homg-growm markup. `T and `t are th becoming , 'f and `F are always , and `D `d are always Th th. This allows one to search the code for "th" and correct these on demand.