The Nikon teleconverters are only compatible with some Nikon lenses. See this chart:

http://www.nikonusa.com/en_INC/IMG/A...omp_chart.html

It looks like the compatibility is determined by the maximum aperture of the lens.
- Nikon autofocus is supposed to work with lenses of maximum aperture f5.6 or wider.
- Put a 1.4x converter on a 70-300 f4.5-f5.6 and it becomes a 100-420 f6.3-f8 i.e. way outside the official limits.
- The situation is the same with any converter. The Nikon one includes a safety feature to stop you making a mistake

Teleconverters are intended for wide-aperture lenses like the 70-210 f2.8.

Having said that - yes I do have a monopod (Manfrotto). I find it is useful in some cases:
- It is almost as cumbersome as carrying a tripod. Useless for situations where you need to compose and shoot quickly with both hands free. I know two people who use a monopod all the time - because they have trembling hands
- It is much less stable than a tripod. It stops up-and-down movement but not rotational movement
- You can't use a monopod (or a tripod) with VR so finally you might not gain anything compared with the lens by itself with VR turned on.

I use it at least once a year for a stage production with a very heavy 80-200mm f2.8 (no VR). I'm sitting down for two hours with the camera+lens supported by the (heavy) monopod zooming in and out according to what's happening on stage. It works pretty well for that.