Typing these characters is quite annoying though. The characters for most programming languages are readily visible on a 108 key keyboard, which means they’re easy to remember and teach.
The main issue is that computers don't come with a standard default layer for math and APL characters anymore so it's a huge leap of faith for someone to start to use these characters.
\in => ∈
\emptyset => ∅
This depends on the implementation. In Dyalog APL for example, the special characters (glyphs) are effected using fairly simple two-key sequences. Mnemonics are used to help learning. I found it fairly straightforward, surprisingly so.