I tried the try for free button.
The run took longer than my attention span. Since I'm not a potential customer, that's not a data point.
On the other hand, adding some text to the code editor page quantifying in minutes and seconds how long running example code will take would be a low effort way to manage user expectations.
Setting the context as a proof of concept is ok. It's honest. Letting people know it will be slow is good because it is honest, too.
Give people evidence that you can be trusted. Javascript that runs on back-button mouse over is not where to put your efforts. Good luck.