Incident Management Systems that include PSIM require independence from manufacturers. It is essential for the well being of the product and those that rely on it.
By being independent owners of projects can ensure that they have the ability to specify the best of breed when in the design phase, they do not need to cut corners buying a poor product when they want to use another from the same stable.
There are other advantages, faster to completion being one, and, more reliable being another. Simply because IMS developers have a larger team dedicated to the interaction of devices and diverse software packages.
Some confuse the simple rules engines adopted by VMS and Access manufacturers as being complementary to those of the specialised IMS designers. This is never the case. Merlin's MRE (Merlin Rules Engine) has a large library supporting many functions from the simple event management to people control, mass notification and an impressive library to link to CCTV and other BMS (building management system).
Of course having a legacy library often means that the IMS can extend the life of older devices often way past their best. For example removing the necessity to maintain older operating system support.