Here’s a link to a consumer review org that actually tested it with standardized loads and measured drying times. They don’t work, takes just as long and cost the same in electricity.

https://www.choice.com.au/home-and-living/laundry-and-cleaning/dryers/articles/dryer-ball-review

It’s sad that nowadays most “reviews” are just going by feelz and not by numbers. The placebo is strong with this category.

The 200% seasonal efficiency is a bit off, Nordic models, measured with the “colder” European climate zone, get 300%+ and have guaranteed output at -25C / -13F. Example model from Mitsubishi:

It’s worse than 5.5x or 4.3x in warmer areas but the right model air source heat pumps work fine down to pretty damned cold. Norway and Sweden have a ton of them as they spend a ton of energy on heating and this saves homeowners a ton of money every year.

Best models optimized for average climate now reach 5.5x or better in the green, moderate zone, SCOP of 4.3 is actually pretty terrible but this one is built to be ice proof.

Example latest bestest heat pump with 6+ seasonal COP: