There can be some reaction to the ascetic acid in it, thus the bumps/tender spots. MC's product uses this to buffer the IGF so that it is more stable and lasts much longer. If they used bacteriostatic water, it would go bad within a couple of days because IGF is a very sensitive molecule once reconstituted.
The pumps are awesome, and it leads to increased hyperplasia which means you get new muscle fibers which you don't lose. Keep in mind that they are new fibers so they start out small. As you work to increase size (called hypertrophy), the addition of these new fibers means you have more fibers growing bigger in size so you increase the overall size of your muscle more in time than you would if you were not using IGF.