I have one that came with my phone. Basically you slip your phone into it and your phone becomes the screen that you view. Half of the screen creates an image for one eye and the other half of the screen creates the image for the other eye, giving you depth perception and 3D... This is quite a good and cheap option for experimenting with because you've got the phone anyway!
Is it any good? ---
In my personal experience there wasn't anything new, anything I hadn't seen before on a PC in some form or Another, except for one thing, and that was watching Michael Watson sing & play a piano in his studio flat I think somewhere in Canada. The recording was in three dimensions it was as if I was stood in the room watching Michael play the piano I Could Turn Around 360 degrees and see his kitchen, his dog, I could see out of the window and a lorry went by. Watching it again many times you could watch different things sometimes I would just watch Michael playing and singing and sometimes I would just watch the dog. It's the most fascinating experience you can imagine it's as if the artist Michael Watson was playing and singing just for me. I was completely transported into his studio. I will never forget the experience.
This was done with a Galaxy S6 Edge and I think it was called an Oculus VR or something...
It could well be this one:-
or it's predecessor (if there is one)
This is an image of michaels studio:-
A very poor substitute for the actual experience but you might get an inkling of what I'm explaining...
When I said there wasn't anything new I meant in the technology. What was new and what was impressive was the feeling of actually being present with Michael as he played and sang Just For Me. This is a first Glimpse at where this new medium can take us and it is fantastic. Imagine, this was done with a bog standard phone and a small plastic receptacle for the phone, and a bit of software. Imagine what will happen, what will be accomplished once they start developing the technology specifically for this application...