For most purposes I prefer a metal hood to a rubber one. Before I lost mine, I used a generic 52mm metal hood made by Kalt with my film cameras and an HN-21 with the D200. (I had the HN-21 for a 75-150mm already, but it's a scarce item).
"There is no real magic in photography, just the sloppy intersection of physics and art." — Kirk Tuck
The HR-2 is just fine, but I don't often use it. The 50/1.8 has the front lens element set so far back from the front of the lens body that it's sort of self-hooded. Most of the time I don't really feel the need of a hood for either flare reduction or physical protection. Plus, it turns a petite lens into a more noticeable one. Still, if you want a hood, the HR-2 gets the job done and has the advantage that you can pop the rubber back for storage or to "de-hood" the lens. And it has filter threads so you can put filters on without removing the hood. (More useful for film bodies, but still...)
Rubber HR2 is a good one, I have that on my AF 50mm f/1.8 lens. The front element on the fifty is fairly well recessed in the body; you could almost do without one. But I do use the HR2. Tip: it accepts front threads so you can use filters with it, though I would prefer to have the filter between the front element and the hood; you can use a 52->62 step up ring and filter the lens that way, too - it will clear the hood and provide some protection - I did this when using the fifty with red, yellow, orange and green filters (for B&W photography).
The metal hood for the AF35mm f/2 lenses will also work.
I'm a little late to this one, but my experience is that the rubber hood protected my lens from damage. My FM swung, and bashed against a concrete park bench. I'm no longer sure of the hood make, probably Nikon, but the rubber absorbed enough of the impact so that only the plastic mounting ring was chipped. Needless to say, I like rubber hoods!
One other great use is that you can place them against glass, to eliminate reflections, and it acts as a bit of a shock absorber, and can steady the camera somewhat.