My experiences have been quite positive. This plugin has been a lifesaver.
Although free always seems better, Naomi has clearly put a lot of work into this plugin. And for many people it removes the need to buy a Gravity Forms Developer License. All in all, this is a commercial-quality plugin that eliminates a $199 purchase. (Indeed, the Gravity Forms Developer License seems well worth the money. But, for people who only need to add Stripe to a website, this is a bargain.
I donated a few weeks ago, and the support from Naomi has been fantastic. I had a couple of small issues which were resolved quickly. I also requested a feature, and it was added to the next release of the plugin within a few days.
People have to eat, and I definitely feel that my donation was well worth the money spent, several times over in fact.