I've been using my cousin's pneumatic squeezer for the last three years, and I figured it was about time I let him have it back. So I bought my own.
You can build an aeroplane without one of these, but man, it sure does make life so much easier.
I got a good deal with Aircraft Tool Supplies. Included with the squeezer was an extra yoke for working on longerons, plus an adjustable piston, so no need to fiddle with spacers to get the right amount of compression.
I also bought a 5-1/2" yoke as well (not shown) for a much longer reach.