Does it come with a rubber/plastic shoe/casing ?
So sorry for the delay in answering!
No, it doesn't come with a boot, but we clip ours to a D-ring. After borrowing this model SPG from my husband for awhile, I decided I needed to have one of my own. It's so easy to read - wouldn't have anything else.
no, it does not.
Yes, I believe you will have to install the housing yourself which is very straight forward.
Yes, As noted in the "What's in the box" heading.
I believe I purchased a boot separately. I think OMS does sell one--and I may have such a boot but couldn't figure out how to use it. My boot was made by some other company, and while the gauge is loose inside it, that doesn't seem to cause any problems.
The standard procedure for divers in my region--Great Lakes, particularly Lake Erie--is to use it without a boot, and rig up a clip on it. I think it's part of the DIR B.S....you wear it on the bottom left-hand side of your BC, and unclip it to look at it. That always looked cumbersome to me, and being an avid gauge watcher have it positioned toward my chest.
Here's some advice, too--I like this gauge a lot. I dive frequently, and it does seem to loosen up eventually and start to leak. All you have to do is replace a small O-ring where it enters the hose, and it's good to go. A dive shop technician told me this is a common--and, as I say, easily corrected--problem with the OMS PSI gauge.
Mine did. Plastic, I think. I left it off though.