Yes, I have owned 2 or 3 of them over the years, sold them and then bought another when I spotted a good deal. For the price on the used market, they were a great lens. I ended up keeping my Tokina 17mm f.3.5 which is wide enough for me. I never took to fisheye images.
I had that same (?) Tokina ( 17mm f/3.5 AT-X 17 AF PRO Aspherical) for Nikon APS-C and it was my most valued possession for years when I first started with photography. Got it super cheap at a Cash Converters (a pawn shop in the UK for those of you elsewhere) and only just sold it recently for a good chunk more than I paid for it. One of my favourite lenses of all time and I think not a very common one.
Again, on a full frame 5.2mm will require only 2 shots to complete a 360. But the resolution or final size of the image will be smaller and likely to have serious color aberration and soft on the edge. On a full frame the ideal size is 12mm, on a aps-c it is 8mm. Unless the crop factor for the future camera will be 2.3