Give it to Nikon to design the world's most horrible in-camera menu system, then design a flash that requires you to use it...
I agree.
A flash without a standalone menu to let it even be operational seems questionable. And having this button on the flash would be much handier than diving into the camera menu. Maybe it was one thing to do that in the SB-300 or SB-400, simple and inexpensive (relatively), and likely owners never intend off camera flash. The price of the SB-500 seems to exceed that reasoning though.
I'm very happy with my two cameras, D800 and D300 now. In Nikon brand, I only have two SB-800 flashes (for ten years), and the flashes perform well and have been very reliable. I don't have the SB-910 to know, but consider the SB-800 the best flash Nikon ever made, it does it all. But I have questioned a thing or two about some of the flash system design quirks (generally meaning some of the basics of the camera metering system for flash).
The TTL vs TTL BL choice should be a camera menu OTHER than the Spot Metering menu. Sometimes it is desirable to turn the default TTL BL mode off. The SB-600, SB-800, SB-900 had this menu on the flash unit, and that was great, but only the SB-910 is still in production with it. It's the good reason I keep my two SB-800. It's fine if Spot metering necessarily switches to TTL, but it is crummy as the only way to do it. Spot metering is very little problem indoors, because unless high ISO, the metered ambient is normally insignificant level to have any effect at all (the flash does not use Spot metering). But then we certainly have to remember to deselect Spot when going outdoors. If outdoors, Spot metering seriously affects the ambient metering, and seems beyond novices.
Since the D-lens distance accuracy is so tremendously poor in zoom lenses (which itself is a don't care to me), then it seems very questionable to override the default TTL BL direct flash metered value because this faulty distance report imagines exposure should be otherwise. That means the TTL BL flash result on a hot shoe extension cord result is often seriously underexposed for that one reason. I have that written up at
Non-Nikon brand flashes bypass the TTL BL Zoom Problems . But this problem can very seriously affect any TTL BL flash picture, depending on the error of the D lens distance. The 16-85 mm DX lens is a nice lens, but it is really bad in this respect (as are other others). The 24-70 f/2.8 is a pricey lens, and it has this problem too.
It only affects default TTL BL direct flash. Not TTL, Not bounce, Not Manual flash.
Ways to work around this D lens issue with TTL BL flash:
Third party flashes do not suffer with this problem because they don't implement the head tilt switch for Nikon to know when to screw it up. The third party flashes don't even know about this problem, but Nikon flashes see it.
With Nikon flashes, FV Lock will bypass this problem (on cameras with FV Lock). FV Lock knows you may re-aim the camera, and simply ignores the D lens distance.
Or Spot Metering selects TTL, which is not affected by D lens data.
I have that problem written up at
Nikon camera TTL BL flash - D-lens distance data accuracy . A camera menu to disable that D lens effect seems very desirable. If we spend thousands of dollars on this gear, we should expect a bit more (more like the early days of Nikon).