Having just gone through this, the top of the radio pod, with Velcro:
1. Virtually flat mounting surface.
2. Mounting surface is cooler - Velcro adhesive stays cooler, SM stays cooler - case, wiring don't fade or get brittle.
3. Easily viewed, yet not obtrusive.
4. No sunshade needed.
5. Doesn't look like a radar detector. RD's are illegal in some states, provinces. RD's are cop magnets.
6. Attracts fewer would be thieves.
7. For street use, you don't need to look at the SM on every blast. If your tune-up is that close to the ragged edge you're probably asking for it.
BTW, Velcro makes a new, special product for vinyl, with a vinyl based adhesive. Finally, something that sticks to dashboards. Far superior to their "industial strength", acrylic based adhesive product.