But each time I suspected I could have done it better and faster manually

There is a class of tasks that can't be done faster manually, unless you're some sort of colour-smells-like-chicken-and-numbers-have-taste genius. And there is other class (my suspicion now is any non-standard task+framework) that are slower than using agents. So I can imagine you have excellent experience with some tasks like USB hacking and would do it faster than LLM. On the other hand for me, as a Java developer, hacking a USB is finally possible with LLM. Otherwise I'd need to stop-and-learn for some time, which I wouldn't, so either I'd by a more expensive hardware that fulfills my requirements, or put the USB reverse engineering project to my 100 acre todo list