I had some issues with the 20th century reel. You have to really make sure the the film is properly caught under the spiral hook, or it will slip off and scratch. I recently snagged a Nikor 2x3 sheet insert to a Nikor tank. It can actually handle 10 sheets which is nice, but its also a bit tricky to load.
The 20th Century reels can be tricky to load if you're not familiar with them. I spent some time loading one with developed negatives in daylight. The two oddities are loading with the emulsion "down" (towards the inside of the spiral), and making sure it's clipped correctly. I have good results by holding the back edges of the spool on both sides with my fingertips, and pressing against the edge of the film with my thumbs. Also makes it easier to feel both the flex, and the "click" as the arm clips the negative.
I've got both the 4x5 and the 2x3, and never had problems with either-- well, not entirely true. When loading the 2x3 reel, because you're loading the "long" way, it's possible for the corners of the film to slip through the ends of the reel if you're not perfectly straight. Easy to correct though, as long as you don't try to muscle the film into place.
