Several months ago I was a Kickstarter backer for a company called GoWorx. The project I backed was for an attachment for your cell phone to use with GoPro attachments. I have been very happy with this product. I've mainly used it with my iPod Touch to help me keep keep it stable when taking a video or photos. I have attached it to either my tripod GoPro mount and my GoPro handler. It is somewhat small and lightweight which makes it easy to travel with. The grip is very good, it holds my devise very snug and I am not worried of it possibly falling out. My only complaint is that the devise can only be in landscape mode, sure you can remedy this by turning your hand if you want portrait position. It would have been nice if they created that tilt feature built in. I still recommend purchasing because of the quality and all that you can do with it.
Here are a couple of the products I mentioned.
GoPro The Handler (Floating Hand Grip)
GoPro Tripod Mounts
FreeRide Phone Mount by GoWorx - 3-in-1 GoPro Mount + Tripod Adapter for iPhone, Galaxy and Smartphones
Below is my Periscope unboxing video that I did several months back. It is a raw and unedited first look at the product. It's Periscope so it was previously recorded with live audience so just ignore my talking to myself and replying to others that you can't see their comments.