"Can a pilot get away with flying an aircraft that he has never flown before, but may be similar to a model he or she has been checked out in?" - Nico V.
“Can a pilot get away with flying an aircraft that he has never flown before – sure, but that doesn’t make it safe. I wonder how his passengers would react if, during the preflight briefing, he informed them that he had never flown that particular model and was not so sure about everything.
Any pilot who flies an airplane and does not know how the systems operate, does not know the emergency procedures or proper speeds for operation is clearly an accident waiting to happen.
However, that very situation you describe still exists today in the US. A pilot who holds a certificate for airplane multi-engine land is legal to fly any piston powered multi-engine land aircraft that does not exceed 12,500 pounds gross weight. It is still up to the pilot to determine how much training he may need.
The best way to ensure your safety when planning to fly an aircraft you have never flown before is to first read the pilots operating handbook cover to cover, then get a thorough check out by a qualified instructor. To do any less is a disservice to you and your passengers.”