The Echo I have (SRM225) has the SpeedFeed head which you just insert the amount of line you want through the holes head, then twist it until it's all pulled in. It's really painless. No dissassembly, spools to mess with or anything.
The downside is, if you're trimming over uneven area, say a rock filled area, as the trimmer bounces around, it's constantly feeding new line, wasting it...
I also don't use the Echo "Cross-Fire" line anymore. Nothing was wrong with it, but I found this stuff at Home Depot that is a line with a protective wrap around it. BFD, right, but this line is like a hot knife through butter, last longer than due to that additional wrap, but the big thing is my speed in trimming. I can fly down the fenceline with this stuff. The Echo line needed more time to cut.