Pleasantly surprised and how well these work for my 100w solar panel on my Taxa Tiger Moth. I prefer non permanent solutions to mounting on this camper since the frame and existing racks are occupied by other gear. The arm portion is flexible enough to be easily adjusted when I want, yet sturdy enough to keep the panel in place.
I am using 2 of the mounts and feel this solution is adequate for a single larger panel. 3 mounts would be ideal especially in the event that one of the vacuum seals fails; one mount would not have enough strength for a panel this large. I did; however, intentionally secure one of the mounts halfway on/off the paper sticker on the back of the panel just to see how the seal would perform and it held with only minimal seal degradation after 30 minutes (half pump to get it back to full seal). Eventually the seal would fail, but it leaves room for user error or imperfectly flat surfaces.
Overall, the price point is worth the solution. I purchased another mount specifically for a weBoost after testing these solar panel/tablet mounts. Last note, I do not suggest driving with the panel mounted as the natural movement during transit would jostle the arm and the panel would hit the vehicle - stationary use only in my opinion.