This is a great product from an interesting company run by divers making products for divers. The text below has been extracted from the Poland based manufacturer/designer SaferDive.com. Our amendments are shown within [ … ] which we trust are faithfull to the intent of the designer.

After a few dives with it you will wonder how you managed without it so far. Practically all the time, with no effort at all, you will have an eye on your partner or another pair of divers. I use this invention also as a diving instruct[ion tool], and I think it significantly raises the safety of my trainees or less experienced colleagues. There is no need to continuously turn around in search of your diving partners. Just a little movement of your wrist … and, since lifting the hand is an extremely characteristic gesture, the couple/ partner following you will see it, and may signal “it’s OK” with their hand or torch. 

• The convex mirror design allows, with no annoying rotation, to quickly see what is going on behind you, and by making small hand movements – also from the side, above and below you. This significantly increases the frequency of contact and thus the security of the team underwater. 
• Inspection of the equipment under the water. Lifting the hand, you check the position of pipes [hoses], checking if nothing is tangled or whether the gas leak that has just been signalled by your partner is really harmless:-)
• The search for a boat without the exhausting turning the head up under water. Positioning the hand in an appropriate way will allow you to see the water surface in front of you and you keep swimming under water, until you see the outline of the hull of the boat. 
• When swimming on the back, e.g. returning to the raft on the surface, you can easily control the direction, without unnecessary extending the distance by missing the target by 50m. 
• Jumping backwards into the water, you can make sure that it is safe, and no-one has suddenly appeared behind you. 
• Advantages of the mirror will be appreciated by divers who dive deeper. In the event of a gas leak at great depths the time needed for the V-drill is a matter of life. With the mirror this becomes trivial — each leak from the bottles or manifold can be found immediately. You just see where the gas is leaking from and close the valve. You do not make the full V-drill. 

After numerous underwater tests we have created a product appreciated for instance by DAN – the 360observe mirror. The product is dedicated to all the lovers and fans of diving, irrespective of how advanced they are. 

• Experienced divers, without losing control over a group, will be able to enjoy the beauty of the underwater world. 
• Less experienced divers, for whom controlling the equipment is still a challenge, will learn effortlessly to take responsibility for their diving companions. 

Advantages:

• A convex mirror catches the image of an extensive area despite its compact size since it is light, raising your hand will be tiring [effortless]
• [Bungee] attaching rubber – the easiest and the most reliable way for attaching the mirror is integrated with your hand so it does not limit you from using your or your partner’s equipment 
• The edge around the mirror protects it from scratching 
• The best quality ABS plastic will not damage your equipment. 
• The 360observe mirror that we have been using under the water for a few years: improves safety and comfort of diving, makes communication easier, allows for a constant and effortless control over a group