the ones any parts store will load you are different concept mechanisms. The tool shown above uses central load. At some parts stores you can find another type that reaches inside the coils, and grabs the coils itself to apply a central load. And they also have a kind that is applied to the outside if the coil - one on each side. I used this last kind when I removed my springs, but I just bought the axial kind shown above to put them back in. Both of the other kinds - those available for free at auto parts stores - rely on some form of grabbing the sloped springs - and friction between the steel coils and the steel brackets on the tool. Personally, I think this is significantly less safe, and if the friction between the tool and the sloped edge of the steel spring slip, these tools can suddenly break loose - releasing a HUGE amount of energy in your face.
This is a good page to read:
http://dazecars.com/dazed/spring.html
The kind above grabs the vehicle support on the outside of the bottom of the coil, and the outside of the top of the coil to compress the spring along it's center. I believe it is significantly safer to use, and worth the $60 to own one. Anyway - thats just my take.