I just got my system installed today, and as an ADT convert, I also had some qualms as to how everything was going to compare, especially the modes.
TWC was able to come out and take over my entire ADT system except for the keypads and the smoke/heat detectors. They preserved all my door, window, and motion sensors (which are all WIRED). This worked perfectly because we have many pets and the motion sensors took some time to dial in when ADT installed them, and the door and window sensors installed by adt are the high quality kind, not just break sensors. We asked about installing an additional motion (from TWC) in the kitchen to provide some extra coverage, but the tech advised us to wait unti their new motion sensors, manufactured by BOSCH, became readily available because they represented a significant improvement over their current offering. That is what i chose to do.
I was skeptical but everything works great. As for the modes, I don't know where you got your techs or contacts but you are unfortunate. My techs were knowledgeable. Here is how my system worked/works:
OLD ADT AWAY:
Perimeter, instant. Motion, Instant. Front door, 60 second delay, basement and back door, instant. 60 Second arm window.
NEW TWC AWAY:
OLD ADT STAY:
Perimeter, instant. Motion, disabled. Front door, 60 seconds, basement and back door instant. Instant Arm.
NEW TWC STAY:
Same except front door instant (better). Also, disabling the basement door is very easy, so we can do laundry without setting off the alarm. Instant Arm.
OLD ADT NIGHT:
Perimeter instant. Motion, 60 second delay. Doors 60 second delay. 60 Second Arm window.
NEW TWC NIGHT:
Perimeter Instant. Motion 60 second delay, doors instant. 120 second arm window.
The TWC is just as I want it.
My tech also told me that you cannot in fact arm AWAY if you do not exit the house. That is, if you arm AWAY and do not trip an exit sensor (door), the system arms in STAY mode because it assumes you didn't actually leave. This makes sense and appears to be true as per testing.
The jury is out on the smoke. I liked having the ADT wired units - it was my understanding that they had their own battery as well as were wired to the ADT panel, which gave them their primary power and which also had a battery. TWC is not allowed to be a "primary monitor" for fire - my tech would not install the smoke system unless my house was up to the applicable fire code. In NYS this means at least one in each sleeping room, and one outside the rooms in the hallway, as well as at least one on any other level. I was warned of this in advance and purchased el cheapo Wal Mart detectors ($3.50 each). I am planning on upgrading them to an interconnected system later.
My only complaint is that they were not able to set up the ability to arm NIGHT from the keypad, which is what I have on the second floor. Thus, I have to arm the NIGHT mode from the touchscreen downstairs before heading up, or arm it with my phone or tablet once I am upstairs. Maybe this is why they give you an extra 60 seconds.
Bottom line, they should be able to configure it how you want it. Mine works like you seem to want yours to. I dont think this has anything to do with it being a takeover; the config is all done with their equipment, not anything from ADT.