Like you said, "different brand", so that's the difference in price.
With the 3M vinyl, it's NOT all about the looks and appearance of it, it's also about the technology they used in the vinyl to ensure that there's no air bubbles.
On the sticky side of the vinyl, theres a grid pattern that's been cut/scored, so if theres air bubbles, you can just push the air through the cut grid and out to the edges.
Unique Comply™ Technology 3M DI-NOC™ Film uses an adhesive system with grid-like channels on the adhesive surface, allowing air to escape during application. Air bubbles trapped between the material and the film can escape along these tracks, making applications to a large and complicated surface easier and ensuring a perfect finish.