Techy? I’m a programmer. I love tech.
Is it worth the time? Depends on the individual. It was for me. It added a lot of value for my home and situation.
Functions it can’t do? It does everything. The interface essentially functions as a keypad. If it’s missing something, then it’s not something that I need.
How to connect? Use AD2Pi, Arduino Mega, and a ThingShield.
Control completely? Yes, I wrote a suite of apps that control it - completely. It turns on and off by itself and many other features all suited for automating the alarm (from my perspective).
Mac? Yes, you just need a web browser and the Arduino compiler.
Pics? I can take some later when I get time.
Ultimately, here’s the issue. If you’re techy, it’s not hard to do. If not, it’s still not hard, but the comfort level won’t be there, so it may not be something the average person wants to do. All of the basic functionality is readily available without coding skills (assuming adding a device type and smart app are a given). If you can code, then customizing the functionality is not an issue. I customized the device type to fix things that I believed were issues (nothing significant, but it works much better now). My apps extend the functionality of my alarm so that it functions completely behind the scenes for me and my family.
My issue with HA in general is this, I have yet to find an app that does exactly what I want, that does it the way I want, and takes into account my situation. Short of simple switches, contacts, or motions, every app written covers a specific set or subset of situations. That said, every app that does what I want typically falls short in one way or another (maybe I want lux taken into account, or presence, or something else). Sometimes things can be accomplished by utilizing multiple apps simultaneously, but there are pros and cons to this approach too. So I have created things that make ST great for me.