The biggest thing I've found is engineers not letting the devices "mesh" for 20 minutes. If you learn them, site them and leave the panel in commissioning mode for 30 mins you are definitely doing yourself a favour.
PIR's are fine, I personally don't get any false alarms as I follow the...
Personally I'd also install a hybrid system using the exisiting cabling where possible. A Texecom can have wireless expanders which lets you use wired/ wireless and is a professional piece of kit with a small amount of complaints.
With an alarm you get what you pay for, and for something that...
If you where looking to do a panel change i'd recommend starting from scratch.
I have ran into a few problems installing the Comms Wi-Fi modules and they are very inconsistant (as is the app). What prurpose would you want it installed for?