Testing your speed with Speed Kit with tests such as Page Speed Insights / GTMetrix / Pingdom will not work properly and will not show you much improvement. Unfortunately, those tests do not take into consideration the fairly new Service Worker technology in the browser, which Speed Kit is built upon.
The main problem here is that for your users the Service Worker will be installed at the first load and then immediately usable on the second load anywhere on your website (and all loads afterward, even when returning to your page later). The tests mentioned above only consider the “first load” of your site and are therefore not able to install and make use of our Speed Kit Service Worker.
Let's look at an example of a normal users visit: He opens your landing page. The speed of this "first load" will be the normal speed of your own server. Then the Speed Kit Service Worker gets installed, right after the page is loaded. Next, the user navigates to another page on your website ("second load"). At this point, Speed Kit is active and will accelerate that page load already. When the user exits your page and comes back, Speed Kit remains activated and will accelerate all future requests to your website.
We recommend using our open-source Page Speed Analyzer  which is based on the open-source WebPageTest  and also tests the second load, showing the full speedup we provide. If you want to test on WebPageTest yourself, remember to "include 2nd load" in the advanced options.
If you are worried about your SEO-rank, keep in mind that Google does not measure website speed in a test environment to determine your rank, but instead uses real user data. This is why your SEO will get the full benefit Speed Kit provides.