I would actually say that is a good attempt, but i agree with some smoother blending, try wet blending if you prefer it. Some of my NMM is also wetblended with a good finish so definately worth doing.
Technically as LTP has said you have a bit too much base colour and since you've taken it up to white as a highlight, i would actually from the stage you're at, glaze some base colour on to smooth the blends first, then i would actually start to glaze with a darker brown to give you more shading, as i think that is what's lacking with the example you've done. Keep reducing the area glazed with the shade colour until some parts are almost a dark brown black, my own technique usually takes me back to black.
There are two things to pursue from here, either a highlighting similar to what you've done where the the point where the light hits the object is the brightest or you could possibly try SE-NMM, which at the lightest point draw a darker line parallel to your higlights to show the reflection of the ground and just highlight it up but going down instead. I know this statement sounds a bit strange but, i have spent time looking at real day metal examples and how light reflects off them and trying to figure out how to paint them well. So you will also notice that the upper areas in NMM are usually darker and the highlights are almost backwards but this is then counter-acted by a fine white highlight which depicts the light being picked up at the edge. Perhaps that is something worth looking more into.
Saying all that i think you are definately on the right tracks to a good NMM. Keep practicing and playing with how light reflects on different surfaces, i think weird shapes are the most challenging and fun to paint compared to flat or cylindrical surfaces. I hope this all helps. Here is an example of one of my first attempts at NMM

so everyone has to start somewhere.
Clicky