Jib sheet block upgrade

My wife crews on our H21SE and mainly handles the jib. She has trouble uncleating the sheet from the wing. It's a new line that does not retain water and runs through the fairlead nicely, a small improvement. She sheets the jib intially after a tack and I end up giving that last good pull, particularly beating with the blocks all the way back in the slides. She then has a tough time uncleating them if the sail is under backwind pressure at the end of a tack. They are the original Harken Big Bullets with spring mount and rotating cam. I also upgraded to the Harken extreme angle fairlead. Not much help.
Has anyone tried the Spinlock PXB powercleat upgrade kit that fits Harken blocks? It replaces the cams with a pattented single cam system and claims to be very easy to cleat-uncleat even under large load.

Spin locks work well but wear quickly. They are also hard on your sheet lines. With the adapter kits they are easy to install. Give them a try or consider flipping your current cams upside down so they lock pulling up and release when line is snapped down.