Your entire fleet should be able to operate with one type of device on the same platform.
Plug and play installation is the only way to go. Hard-wiring requires installers and costs more money.
Your provider should have competitive pricing with features that solve your problems.
The platform should be simple to use and require little or no training.
The platform should be usable by your entire workforce. iPhone, Android, any recent device should be able to use the platform.