It's better to use your own video! using other people's creatives to promote your product without their authorization means that you’re infringing in their copyright! It's possible to face a DMCA takedown notice or even a lawsuit if you’re infringing on other people's copyright. Aside from obvious Copyright issues, there is the issue of ad fatigue. If a video has been seen multiple times by the same audience, people get tired from seeing that video. Ad fatigue reduces ad performance such as the video click through rate.  If you are using someone else creatively which they have overly promoted. You might experience a low ad performance.