My apologies, I had not been watching this thread so did not receive notifications.
Anyway, sometime last year I believe, I picked up a few add-ons from Extra License with the intention to shift them to being free and open source. It seems I did not get round to doing that with all of them, so this one has been redirecting to a purchase page mistakenly. If you purchased this add-on in the last year or so, feel free to get in touch and I'll sort out a refund for you.
In the meantime, I'll publish the actual working version that I seemingly forgot to do. My bad.