It's just the equivalent of a lens hood, there's no glass in either that one or the mini 3 pro version. Without it you will get more lens flare. Before you gum things up with blobs of glue: get a magnifying glass and check out the four locking...
Yes, They need a few batteries and a good plan, but between "cuts" its adequate for their needs. Some of them "stack" a bigger homemade battery on it to get past the 20 min mark.