They do need to bed in for the first hundred miles or so but the pedal should not be affected that much and they should definately not be spongy.

If the brake pedal firms up with a few presses then there is air in the system that needs to be bleed out. Take it back. FYI Although I don't normally use KwikFit they do a brake fluid change for £35 which is very good value and worth considering if your fluid is over 2 years old.

 

Another possibility is that they've fitted the springs backwards. I did this once and they then push the pads too far away from the disk when you take your foot off the pedal. Next time you come to use them the first half of the pedal travel is simply moving the pads back into contact with the disks...