I just switched from Simon XT to Qolsys 2+. The sensors transferred over easily. After being on Simon et al for 17 years the Qolsys is very different in a modern way.
I had The Simon XT itself in a secure hidden location with keypads, a touchscreen, key fobs and an interior siren wired to the XT. The Qolsys IQ panel is also in the secure location requiring control to be with Remotes and key fobs.
Having had numerous business experiences with alarms and thieves, the first thing they go for is the alarm panel and communications. Sirens being next. Question this new generation of table top alarm systems.
With Qolsys there aren’t any keypads I’ve found, only Qolsys remotes of which you can connect three. Unlike Simon keypads the remotes require AC power. The Simon could drive an external siren directly, Qolsys can but will require a 12v 300ma power supply.
Interlogix shutting down is the last nail in Simons coffin. I had bought a Simon XTi-5 version 2 panel. Turns out version 2 was the start of Interlogix encryption and Only worked on version 2 touchscreens and no touch pads. Not documented either. After wasting a weekend troubleshooting, returned it and bid farewell to Simon.
Good Luck