Really sorry to hear your first impression wasn't great @altdataseller It has to do with limitations around performance/memory. In some instances, loading large documents in multiple iframes at the same time could cause mobile safari to crash. We have plans on how to address this, but we thought that seeing as frontend responsive testing is most likely going to be done on a Desktop-like device, we would prevent possibly crashing your mobile browser and show you a video walkthrough of how it works on desktop. Happy to chat more about this offline if you want: hello@viewport-tester.com