So what is the advantage of a kayak for fishing over a flat bottom aluminum? I have made many trips down our creeks in a flat bottom with a comfortable seat and have never flipped one.
Kayaks are narrower and can get into places you would have difficulty going in a flat bottom boat. Thay are also much faster (unless of course you have a motor) than a flat bottom aluminum. They are also lighter and much easier transported. A kayak can go all day in 6" of water. Can also slide it over logs and stuff in a creek. No question about a flat bottom boat being more stable and comfortable though. Sort of like comparing a motorcycle to a pick up truck. I've rolled mine several times and and except for the one instance I was sliding over a beaver dam it was when I was getting in or out.
That all sounds reasonable. But floating down stream, I can't see that the kayak being faster is worth much. I guess if you were moving up stream it would help a lot.
Somewhere round the half way point u have have to go back
Only if you go by yourself. If you go with someone else, you leave a vehicle at the take out point and then drive to your launch. Of course after the trip, you have to go retrieve the vehicle from the launch point. Or you have someone drop you off at the launch point and then come to get you later at the take out point.