I prefer the spool.
I can reuse them to store other lines on too.
I also tend to keep the boxes to house the old lines in.
I suppose i may be the odd one out, collecting old lines, but they are usually ok and i've normally changed them, to try something else
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Mind you i suppose if you were to supply them in a paper bag, then it would be very Ecco friendly.
I also like having all the details of the line on the box, and keep them for reference.
I would wonder at whether or not being stored in a polythene bag, might have an effect on a pvc line, being similar materials, would there be a possibility of trans-molecular migration?, i'm no chemist though, but i've had problems before with soft plastic baits melding into plastic boxes, many moons ago, and wonder if something similar might happen if the lines were stored for a period of time. I'm probably speaking complete tosh mind
Sandy