We occasionally get asked whether Zuko tracking affects page load speeds. As mentioned in the Zuko technical information, the javascript we use is very small (4.7kb transferred) so we have never had any load issues reported by our clients.
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That said, to assess the possible effect of loading Zuko javascript on a form we ran a series of tests across four different forms*. This involved loading the form with and without Zuko tracking and logging the average time differential between the two:

From this, we can see that there is generally a minimal impact on page load when using Zuko. Of course, the best way to reassure yourself about performance issues would be to run your own test - we'd urge you to do that to demonstrate that Zuko will not adversely affect the user experience.

*Test was run 20 times with and 20 times without Zuko and the average figure is calculated using the mean. The tests were conducted using the Chrome and Firefox browsers at a ratio of 1:1.