Of course, that's when you're using them as intended. As for using them far below the glow level, there shouldnt' be any difference. I'd characterize the filament against that of a standard lamp just to see how they compare. Just start with low voltages and measure current each time using a DC supply and then use Ohm's law to calculate the resistance and create a graph for comparison. I can see where using a halogen lamp in place of a standard 150-watt incandescent lamp would have some space-saving advantages. Still, with the smaller envelope, you'll have to watch the heat and mount the thing accordingly.
Dean