I felt obligated to give this a try due to it having a fair few downloads and only one heavily negative but vaguely non-worded review. Ultimately I think it has potential but it's lacking in some areas. Here's my personal points from my use of it.

Pros: Looks good. Interface is more stylish and functional by appearance than, say, DeoVR (which is my main point of comparison honestly). Built in browser is functional. Has settings for side by side, 180/360 views, resizing/zooming, and so on. Had no issue with either PNG or JEPG (I can't say the same for DeoVR which refuses to even acknowledge JPEGs)

Cons: A space above the browser seemed to be for ads or something? Not saying it can't have ads, but boy is it jarring for a VR app. No webm support. (I didn't test gif either come to think of it...) Could not get videos to work in general - it popped up a loading bar saying it had to load them first, and never did, just sat there doing nothing with an empty progress bar. Side by side 3D is missing the option to flip the sides, which is essential - in DeoVR I can do that which I had to do for my test images to make them properly 3D, but in Gizmo it's not an option. I'd have to manually edit the image.

Verdict - the look of it is nice and could be a very useful VR player, but with some features missing and others not working right I can't see myself using it going forward, unless it updates to address these things. It definitely could, there's competence here I can plainly see, but in its current state it's just not enough.