The cons are 2.5" is too much for a 250 and you will get a certain amount of bumpsteer with just spacers. The F250 sits 1" lower in the rear than a F350 and my 350 worked out to be exactly level with a 2.5" spacer. If you want a level 250 you will need to swap out the rear blocks for 350 blocks.
You will need new shocks which adds quite a bit to the price. Ride quality will suffer but I don't find it to be unacceptable. The front axle will also shift to the left approximately 3/8" unless you get an adjustable track bar or relocating bracket. You should still be able to get the alignment within allowwable specs.
The pros of the spacers are they are cheap in comparison to a complete kit and the leveled out look is awesome!