UserGuiding script loads itself asynchronously, so it doesn't increase or decrease your web platform speed.
Besides that, we regularly benchmark our application's effects on website speed and overall application performance and we are doing great on that aspect.
We also have CI (Continuous Integration) processes where automated tests are run and manual QA (Quality Assurance) processes before each release to prevent bugs.
Even if you encounter a bug, we provide instant chat and email support where you can keep track of the resolution implementation progress.