Seiko has instructed to loosely take-up vinyl prints, and use tension on heavier media only. The telescoping is more pronounced with narrow media such as 30". Seiko has special flanges to prevent telescoping at the rewind for some older models but not the M. Seiko wants you to use a core with a length greater than the width of your print substrate because they expect telescoping at the take-up. As stated above, telescoping can be corrected after removing the print from the take-up, and in my experience it doesn't affect printing at all. When I evaluated the M with Seiko personnel, I ran 150' continuously with zero deviation in the side margin- even though the media was very telescoped on the take-up.
The colors are great running CMYLcLmK+Gray!
I have noticed that the pinch wheels are leaving what look like to be cyan marks on the media. The M that ran at ISA last week had the cyan marks as well... techs haven't figured it out yet to my knowledge.
It's a great printer though!