I'm one of those that started using a ball machine with a set of Tretorn micro-x balls. I concur with the other folks here: they felt like hitting rocks! I quickly developed tennis elbow and switched back to regular balls
. The micro-x definitely felt harder than any regular balls I had used. I can't compare to other pressureless brands, though.
To avoid spending a fortune on regular balls, I re-pressurize my existing balls with a couple of PressureBall
tubes. They do work well, and they are a LOT cheaper than the commercial re-pressurizing kegs. There are a few other threads on PressureBall in this forum.