Limited options for maintenance on the Phenom although I'm led to believe this is improving.
Mustang very reliable and easy to maintain. Getting more difficult as Cessna drive out authorised service centres to take all mx in house.
Usual Citation landing gear corrosion issues so good winter cleaning program required.
Not sure what level of OEM support you'd get on the Phenom when handlers prang the bog cart into your jet.
Not sure what engine program you'd get on the Phenom but Cessna wouldn't allow PWC to run a program for the 615 so you'd have to use Cessna's Power Advantage. I'd just pay money into a standalone account and give the programs a miss however bean counters can dip in and leave you stuffed when you reach 3500 hours.