For me, it is far better to make my own kits rather than purchase pre-packaged items and for two main reasons:
1) Most people are so price-conscious these days that companies are forced to skimp on quality in order to stay in business. So I buy high-quality individual items and combine them for my own kits.
2) I've never seen a kit that contains what I need for my particular environment and lifestyle
I agree on both points, but don't entirely dismiss pre-assembled kits as a means of building your own. For example, start with a decent FAK and a PSK then build-up from there.
When I was new I looked at the stuff for sale and said "no way, I can do that for less." Turns out it cost me more, much more, but it was tailored to the types of risks I felt were most probable.