Knitters at home who do not wind a lot of yarn, only need to use one of the plastic ball winders.
Because they are not winding a large number of balls each day, they will probably never overstress the unit and they should be able to enjoy the ball winder for a very long time.
They need to make sure they do not overload the ball winder with heavy loads, however. In addition, they should orient the winder in a sideways position on the corner of a table so the metal guide is facing directly toward the swift and not aimed toward the back of the table (as it would be if the clamp is mounted on the front edge of the table). This positioning will reduce the tension and load on the gear system. Also, they should make sure the yarn on the swift is not too tight. That also places an unnecessary load on the gear system.
The most popular unit has been the blue and white unit made by Royal. But the user should consider all of the plastic winders. Don't experiment with new models that have not been properly tested in the marketplace, however - select a proven design instead.
Yarn shops need equipment that will hold up to repeated and heavy use that can wind varying amounts of yarn. They realistically need a sturdy unit that can also wind big balls.
They should use a wooden ball winder, or a large plastic winder like the Jumbo Royal* (or equivalent), or a heavy duty motorized winder (but not the Boye unit which is too weak and noisy).
If they need to also measure yarn length while winding, then they only have one choice in manufacturers - Nancy's Knit Knacks.
Professional users are a lot like yarn shops. Although they may or may not wind as many balls, they cannot tolerate tools that fail.
They need heavy duty wooden tools or the jumbo winder by Royal (or equivalent). They would also benefit by using the motorized ball winders.
Universities and other educational users also need rugged heavy duty equipment, just like professionals and yarn shops.
* - it is not clear that the Jumbo Royal Ball Winder is still available. I have heard rumors that this model was discontinued but this has not been verified.
Therefore, the recommendations I am providing are pretty straightforward:
Knitters at home should buy lower cost plastic winders (they do not require commercial grade equipment unless they simply want to own the best available and can justify the purchase).
All professionals, shops, and institutions should only buy wooden or heavy duty plastic units.
I have seen some shops buy 3-4 small plastic units per year because they wore them out, whereas, had they purchased one heavy duty unit, they would not have been forced to replace it.
Make your purchase selection based on your intended use of the tool and not on the price.
Questions? email me