You change the blunt blade in your wet razor to get a closer, smoother & more comfortable shave. It's the same when replacing the foil with its new sharp blades on your electric razor, the difference being noticed immediately. I change mine approximately every 12 months & it's money well spent.
Where to obtain shaver spares locally is not always an easy question to answer. I found ShaverSpares from an on-line search and placed my order using their parts identification process. The parts arrived next day by 1st Class post. Excellent service in my view.