I've used varying types of helmet or sunglass mirrors, and this one seems to be the most durable and versatile. The flexible neck holds the mirror in place, and there are plenty of ways to adjust, including at the adhesive mount and at the mirror itself for fine-tuned angles. Even with all the adjustment points, it holds it's angle well - the one downside I found was that the mirror is built to pop out, and sometimes did without my knowledge while moving my helmet around off the bike. Would be nice to be able to order an extra mirror piece in case the original gets scratched or lost.
Overall, I found it to be a critical piece of gear for highway riding and I used it the entire trip - highly recommended.