save the money, the C clamp works, but truthfully if you need a clamp to accomplish the compression, you have hidden problems of a more serious nature that should have been addressed prior to compressing the piston....
With the cover off the master cylinder, finger pressure alone should be more than enough, but commonly folks tend not to clean the extended piston meticulously prior to that step, therefore they have contaminents being scrubbed during the compression, making the seals compromised, and in the least, contaminated and difficult to deal with.
Pay close attention to this step, and clean the piston well and you should see what I am saying.
