Models by John is very excited to have some of theses very precise prop balancers. They're a very solid design and should last many, many years with proper care. The stock units will swing props as big as 6", and can be easily modified to swing larger props. I'll be making extension kits for the unit shortly and projected cost is $2.00 per upgrade.
Out of the box, this unit is quite accurate for ducted fan rotors and 6" props. I am providing the items to reduce the magnet strength and boost sensitivity for light weight props it at no extra charge. This modification takes 10 seconds to perform, is not permanent, and makes the unit very very sensitive yet strong enough to even hold up the big 90 mm fan impellor.

Price CDN$25 plus 8% PST if you are a resident of Ontario, Canada