I use a 50' long line much in the manner you describe, though I don't hook it to the collar at all. I use mine with a Ruffwear "webmaster" harness so I can loop it through the loop that's the furthest back, tie it to the handle and then hook it to the metal ring. As you describe, it keeps the line out from underfoot. Even so, you are very correct in your assessment of the need for mad ninja-skills in the beginning

A couple of long-line caveats: Hold the handle; don't grab the line itself if the dog takes off after something, it WILL rip your hand open no matter how soft it is. Step on it instead.

Also, make sure the dog is under fairly reliable vocal control. My dog is great about this. He even understands whistle commands and hand signals. Even so, I have caught air at the end of the line during moments of inattention(my own fault, and that of the damned squirrels!). I can't imagine what a mess it would be with an untrained dog.

I tend to use the line as just a 'back up' sort of thing. I treat the situation as I would if my dog were off-lead entirely. I use an e-collar and I pay close attention.

I LOVE the long line and the freedom and security it allows.