For C-K's P25 system? Coverage. Went from EDACS ProVoice for PD. Analog for Fire to P25 Encrypted. All they really did was flashed all the old Harris M7100's (P7200's/P5400 for portables) for P25 trunking and DES-OFB. Fire uses Kenwood NX radios in analog to talk to the truck VR's. System had lots of coverage gaps from the start and they figured going "digital" from provoice would fix everything. But its worse with P25 then on EDACS.
As for EMS/OPP, from what I've been told, same deal. Coverage issues. Places they could transmit from on the Tait radios in UHF they can't now with the APX in 700 MHz.
That, with a lot of transmissions coming over all digital so the PCC/CACC can't copy a unit, or they dont get the transmission at all.
Plus, just about everyone hates the long antennas on the APX radios. Saw an OPP officer sitting in her car and the antenna was little bit past her ear. Maybe them having the radios up on their vest isn't the best of spots?