Flew a 421B with 900hr a side engines(1200tbo) all around Europe/USA for 2 Summers plus 2 Transatlantic crossings. No engine problems whatsoever. If you get good ones that have not been abused and look after them you will get King Air performance at much less than half the price.
Dont let them idle too slow, you can actually HEAR the gear drives slapping around at low idle.
IMHO they are not a short trip aeroplane. Operations involving multiple short sectors and you are asking for a heavy bill at best.
One inch per minute or per 1000 feet mp reduction on descent whichever is longer, ALWAYS making sure that CHT stays in the green(pref right in the middle)
Allow extra distance and use cruise descents with a level segment to get the drag out and slow the A/c with minimum throttle changes to touchdown.
On my 421 I touched the props 3 times. After T/off to the top of the green arc for climb pwr. Set cruise at 1800(least resonance speed and luvly and quiet for the pax) and dont touch em again till on the deck, fully forward and start the stopwatch. I used to time 5 minutes at idle before shut down to let the turbos cool down otherwise oil gets baked on the shaft resulting in ....well its expensive anyway.
They are great engines, and they will run like clockwork if you are nice to them.
BTW the 421flight Safety course is really good(but expensive)
I have their manuals if you need any bits of technical info on 400 series Cessnas.