I have a 30 foot, before I bought the reel, I would roll the cover up while getting into the pool myself, it was a bit of work since it's so cumbersome and big - a lot of side to side travel, then i would just toss it over the edge on the far end where I mounted about 6 large hooks on the uprights on which it would sit, to get it back on, from inside the pool I would reach over, starting on one end, get it back up on top and unroll it.
With the reel, my life has become really easy managing this mamoth plastic sheet.
I would have to say that an 18 foot cover would be REALLY easy to roll up and unroll since it would only weigh about 1/3 of mine, judging from how mine rolled up, I would have to say that side to side travel while rolling it up would be very minimal on an 18 foot.
I would NOT live without it, it raises the temperature enough to get about 2-3 weeks extra out of a season. It keeps enough heat in over night so the pool is nice and swimmable early in the morning. It pretty much stops evaporation which is a REALLY important aspect for me, being on a well.
We don't have any trees nearby, so dirt collecting on top is a non issue.
For some reason, it also really cuts down on the birds using my pool as a toilet.