And now for the sensible answer;
So long as tire sizes are correct and performance ratings (Y) are matched you will not experience any problems when the car is used for normal road use. However, there are some cheap tires around made from very hard compounds which affect handling whether mixed or not. Tire temperatures will not be an issue so long as performance rating (Y) is adhered to. Its sometimes neccesary to put different ones on the back due to availability. Some folks feel they have to have the most expensive brands, but they are only paying for the name on the sidewall. Of course, you must never mix tires on the same axle.
Good Luck
Steve - UK