I am going to attempt to respond to each point in your last post. Hopefuly i don’t ramble to much.
I get the concerns around the price. When I was trying to figure out what system to get price was a big gateing factor for me as well. Ultimately I got the ADT Security Panel on sale for $299 and I also waited for sales to buy the sensors needed. I ended up getting all of my door/window sensors for 19.99. The ADT sensor prices are pretty reasonable tough. Prior to getting the ADT Smart thing panel I was looking at just getting sensor and using SHM with Smartthings. From when i was looking at Amazon pretty much all of the chearper sensors were about the same price as the ADT sensor, allot of sensors cost more though. So it is unlikely just to buy zwave or zigbee sensors and beat the price of the ADT sensors much at all. I looked at Simpli Safe and their door sensors appeard to be a bit cheaper at $15, I also looked at Abode and i think they were $25. I believe they all align.
If you use one of the other security systems they will use the cloud for integration with Smartthings for everything. The ADT Panel and it’s componets acctually function local. That doesnt mean that all of the stuff you want to automate will be independent of the Cloud though. Simply example is the ADT Tools component will run in samsungs cloud. Then the difference is do you have to go between clouds or just from your ADT panel to samsungs cloud. It would be nice if someone with Simpli Save or Abode could talk to how their sensors are presented to Smartthings. The adt sensors appear just like any other sensor and run locally so to smartthings there is no difference between them and any thing else.
The ADT Branded sensors really aren’t out of line with costs for not ADT sensors. The big differnce is that the some ADT Sensors use a different wireless frequency and use enhanced encryption. This is why you have to have a ADT Security hub for the Door/window sensors and the motion sensors. The claim is that this improves there reliability and range. Last thing you want to do is deal with allot of false alarms becuase a zigbee sensor drops off the network. There are also well documented security vulnerabilities that are potential with Zigbee and Zwaved
ADT has two official apps in the store. The first one is for doing notification when the alarm is armed and something happens. The second is for some smart actions with your AC when smoke or carbon mononxide alert is triggered.
To expand beyond that there is the ADT Tools smart app that allows you to manage many different actions. It has several things it integrates. to name a few
Custom notification with alarm mode changes
Perform certain actions when alarm is triggered.
Change mode with virtual momentary buttons.
Because the Chage mode part integrates with Virtual Momentary buttons this allow other automations to do actions based on those button pushes.
There is a ton of potential automation that comes from ADT Tools. The best part is that if you do find a gap in what it can do let me know and there is a decent chance I can get the function added in short order.