I've got the red one, its pretty well suited for 12-15lb line and does exactly what you'd expect. There was a member here a little while ago Joe who had just decided to take up carp fishing (also know the gentleman from work) he'd spooled up his reels wrong, basically put a 90 degree twist throughout the entire spool. Rather than reloading the spool I suggested we tried using my spindoctor out since we were first on the venue tha day, tied it on and absolutely wanged it out across the entire length of the lake, did that twice and problem completely solved so they definately do work