I used to use in-line spinners often many years ago when I first started fishing. They catch fish for sure. Most of the time, a little snap of the rod tip will get them spinning, but that can be a pain. I also got tired of snagging and losing them, or the hooks rusted and I just didn't bother to replace them.
I think that my use of them declined more to changes in my home waters over the years, specifically drastic increases is SAVs (native and invasive). Having to clean weeds off my lures all the time is a pain, but with in-line spinners, when algae or stringy weeds get caught in the clevis, they don't work, and when that happens almost every cast no matter what you do, time to clip that lure off. But, that can be said of in-line spinners in general with regard to my lack of use of them any more, with an exception on my part when targeting musky, pike, or any of the salmonids of the Great Lakes. Safety pin style spinners are a different story, and my use of them is to target larger species, especially bass.
Betta, just to understand your goal, this box/kit is mainly something you'd like to have with you for any occasion, not just a planned fishing trip, right? Good call keeping it simple. If you live in a warm climate, be careful about storing your box in a car or something though. Vehicles get very hot. And some lures, like hard plastic minnow baits (like Rebel minnows or crawfish), will expand and split right down the back, and they never seem to work right after that.
Another suggestion, if you are out in the field and drop the box in the water, or it rains, or you wade into deep water, and water gets inside your box, then when you get home, you should dry it out and all of the lures, hooks, etc. that may rust. In addition to rusty hooks and blades, the rust will get all over your box and it's a pain to clean. Another solution is that they sell water tight vest tackle boxes now, something to think about down the road.