A “store bought” survival kit is NEVER going to be better than the one you build yourself. When you build your own survival kit you know exactly which items you have, their quality and intended purpose. You also know why the items are in the kit and probably how to use them.
However, if you (like most people) have been planning to put one together for years and still haven’t, bite the bullet and buy one. ANY survival kit is better than no survival kit. Once you get your premade survival kit you can open it up and use it as a base kit to add to and customize.