I am a longtime stereo photography hobbyist and 3-D film enthusiast. I don't do a lot of pure VR—no roller coasters or haunted castles or deep sea exploring games for me. I mainly use Cardboard/simple VR as a 3-D movie delivery system. Any VR system I try must allow me to watch my personal collection of SBS 3-D videos in comfort and ease without disturbing my wife, who does not share my unbounded enthusiasm for stereo cinema and prefers to read or sleep in the bed next to me.
Over the past two years, I have tried seven or eight simple VR headsets, few of which have met my expectations. The problems fall into several categories: too much magnification, too little magnification, chromatic aberration, bad focus at the edges, bad focus all around, flimsy construction, dodgy mechanisms for cradling the phone, etc.
I was actually in the process of designing my own, one-off VR headset as a personal project when I learned about the Homido Grab. I read the specs, liked the photos I saw, and decided to leap in and buy one.
I can tell you right now, the Homido Grab is not absolutely flawless, but it is the best VR headset I personally have owned and used.
It is sturdy and lightweight. It does not employ a headband of any kind—it is meant to be handheld, and presumably passed from one enthusiastic user to another, so that several may share the experience. I am using the Homido Grab to watch feature-length stereoscopic movies, and despite the absence of a headband or head strap, I have experienced no fatigue holding this compact viewer upwards of 90 minutes at a time.
The Homido Grab uses a gentle spring clamp to grip the phone at three points, one at top and two at bottom. My LG G3 fits comfortably. While the clamps are secure, I sense they are not putting a crushing pressure on my phone, which for me is an important consideration.
The hinged door into which the phone is placed latches shut with a magnet. It takes a firm tug to open the door, so I am very confident my phone will never fall out by accident.
I read somewhere that the lenses are a 60mm focal length, which if true is a little long compared to the lenses in other Cardboard-type devices (~45 mm). They are simple biconvex lenses, apparently molded specifically by and for Homido. While they are not made of glass, which I would prefer, they are better than many another lens I have encountered in VR. They magnify my SBS videos impressively, filling much of my field of view while still allowing me an unobstructed view of the left and right edges of the frame. I have had occasion to watch several 'Scope-ratio stereoscopic films in the past several days (namely SEPTEMBER STORM, THE BUBBLE and RATATOUILLE), and all three looked very impressive indeed.
Although the I/A (interaxial, or lens separation) is fixed, I have had absolutely no problems with fusion on my screen. (The LG G3 screen is ~ 120 mm or 4.75 inches wide, which means a center-to-center distance of about 60 mm. Your ability to fuse stereo pairs may possibly be hampered if your screen width is above, say, 130 mm.)
I do have one big caveat: The optics have evidently been designed to impart a soft focus, presumably to minimize the "screen door effect" that occurs when some cell phone screens are viewed under magnification. Me, I don't prefer to watch movies that are even a tad blurry, so I have taken to holding the door open very slightly with my finger—say four or five millimeters. This makes the image very sharp indeed, and while the screen is now tilted in relation to the lenses and to my eyes, this has not posed any problems.
I wish Homido would come out with a variation on this design that incorporates adjustable focus. Then I will feel I have finally found my perfect viewing device. But until that time, Homido Grab has made itself my favorite in the Google Cardboard/simple VR headset sweepstakes, and I cheerfully commend it to you.