Have you even read the AFM on the Limitations with the halo kit installed? The halo kit does require more equiptment to be installed. http://www.centex.aero/halo-250
This is a link to the STC.
Here is the required safety equiptment to be installed:
Takeoff Trim Warning,
Engine Fire Extinguisher System,
Stall Warning Ice Mode.
Emergency Cabin Lighting.
Escape Path Markings.
So less safe? mmmmm dont think so.
Its true you will need more runway when you are operating in the 13,420lbs range but lets be honest, the only time this is going to happen is when extra fuel is required to go farther, as your max landing weight is still 12,500. When the large distances are being covered its going to be a 5000+ foot runway on either end most likely.
45 KTAS is huge! If you do 100 250nm flights that aprox 13.5 hours saved. You also do not need to climb to FL350 to see these numbers. This plane has huge range with the Halo kit. If you are flying from 5000' strip to 5000' strip you would have no problem fueling right up and going a stupid distance.(obviously there would be restrictions on smaller runways)...
My 2 cents.
BEW of BE20s flying in Alberta is aprox 8100lbs - 8600lbs this means a useful load of 4400 - 3900 lbs.
The BEW of Kingair 250s are aprox 8800 (bigger engines my guess). at a 13,420 lbs Gross weight thats at least 4,620 useful load. Now keep in mind the basic empty weights that they have out there include all the furnishings and big leather seats. I would suspect a medivac configured aircraft would weigh less. So lets say 8500lbs thats would make a usful load 4920lbs. sooooo definetly better so long as you burn at least 900lbs of fuel in your flight. and still better if you only burn a normal 650-700lbs per flight.