Several weeks ago I was providing some instruction in a Cessna 421 B to a new hire in a charter operation. About twenty minutes into the flight, we experienced a depressurization when the left windshield blew out, taking the glareshield and top of the instrument panel with it.
In the weeks that have followed, I learned that a number of these incidents have occurred, nearly identical in nature. The new replacement windshields are considerably thicker, and must be custom drilled and fitted to the airplane. The original factory windscreens weren't that way, however. They were made by an outside vendor, predrilled, and the screw holes weren't necessarily centered. We found that the screws were corroded, that they impinged on the windshield, and over time the expansion and contraction most likely lead to cracking which caused the failure under pressure (it was rather explosive).
What Next's comments are accurate regarding the airplane.
The Cessna 421 has marginally better performance than a Cessna 414...but neither one has stellar single engine performance. With full fuel there's a very small payload. Three adults and enough fuel to go very far will max the airplane out...and at those weights, single engine performance is very low.
The geared engines are a known quantity. Very easy to damage. Properly flown, they're great...but if the airplane is going to be flown by multiple pilots, watch out. Someone who gets in there with poor habits such as letting the slipstream drive the engine instead of maintaining positive engine power, is going to do some damage. It may not show up when they're in the airplane, but soon thereafter the engine will be making metal.