Only downsides are the price and a perception "It's only got one engine".
That's not a perception.
It is a REALITY.
Recently an operator conducted an informal survey of PT6 operators (King Airs) and the results of those who confirmed an engine failure was surprising at best. One operator confirmed 2 failures. The problem is that the FAA does not track failures, only fires and accidents. It is a statistical possibility that a PC-12 will suffer an engine failure: that makes it a certainty, with time. Minimizing this is a disservice to the OP.