It depends if you would like to fly the Phantom with a parachute AND its camera or not.
The camera and gimbal on the Phantom 3 is about 234 grams. If you don't need the camera, a system like the Safetech ST60X (220 grams) plus the weight of a triggering system like the Mayday (14 grams) will weigh a total of... 234 grams ! So it would fly as usual.
But you may probably more interested in flying it with its camera. In this case, the total payload weight of the Phantom would be : 234 * 2 = 468 grams. While not recommended, flying the Phantom with a 468 grams payload is technically feasible. There are reports from people flying their Phantom 3 with a 440 grams payload but only for 12 minutes. Please be aware that the Phantom 3 is not designed for this payload. This will wear your battery faster, run your motors hotter, and the behavior in flight could be quite different, the throttle for example would be more sensitive and the battery will drain faster when close to its minimum voltage. It would be better in this configuration to avoid flying on windy days. The sport mode of the Phantom is more suitable to this kinf of flight
The good news is that on the Phantom 3 you may cut the motors mid-flight with a Combination Stick Command (CSC). This drone does not require an extra system to cut the motors. The image below explains the (CSC) for emergency shut down :
Regarding the Inspire, no problem of course if you choose a system specifically designed for this drone. You just need to find a convenient way to swap the parachute from Phantom to Inspire.
Have fun and fly safe !