Love this! The HTC M9 is a beautiful phone, but I have a lot of issues with the battery lasting just for part of they day. When I am at the office I have it plugged in, so it is not an issue, but when I am off, like on the weekend and running around and not able to plug in, the battery is at 50% by noon. This battery extender is a life saver. In the past, I have used a power bank, which means I have to carry a cord to connect the power bank to my phone, so that is added inconvenience. Also, it is awkward to use my phone when it is plugged into the power bank. This here is a great alternative since I am able to (very easily) slide my phone into the case, making it feel like I am just carrying my phone, instead of three items. It is very light weight and adds a little length, but I don't find it an issue. I have used products similar like this in the past and this one is very slim compared to others, which where bulkier and heavier. I received a discount on this product in exchange for an honest review.