Building strength after long period of illness injury

i bought this to try and help rebuild my core strength. After a little no period of injury my core strength is nearly gone, so I bought this hoping to gently build it back up again. I was a bit daunted by the impossibly perfect people photographed on the front of the box with incredible six packs, but decided it was worth a try.  When it arrived I tried it out, even on low levels of intensity you can see the muscles contracting. I expected it to be painful or uncomfortable, it actually feels quite relaxing, like a massage. Even at the highest level of intensity it feels weird but not painful. I think if I use this regularly it will do the trick, the only thing I would improve are the instructions, I would have liked a more detailed description of how you decide where to put the patches.