We've operated the Nextant 400XT for 6 years now and have found it to be really good.
The Williams TAP engine program and Collins CASP coverage help smooth out the maintenance costs. With the new engines we climb to FL400 - FL430 direct with no real issues. The owners require a plane that operates in and out of 3000' runways and we do that with very little issue at temps around 30 - 35 Celsius.
With the new updates the claimed range is 2000 nm, but in saying that the furthest I have pushed her is 1860nm and landed with around 50 mins of fuel.
Proline 21 is a very nice upgrade, also slowly aging though. But is more than capable and the electronic charts are excellent.
Cons form our side, lav isn't great especially with the extended range now, over wing refueling is slow but not the worst.