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I used mine (DGM Optics NPB Filter) again on the weekend, in both my scope (10" dob) and hector (20" dob). I used it on the Tarantula (NGC2070) and a nice planetary NGC246 in Cetus.
On NGC2070, the filter showed wisps of nebulosity that couldn't be seen without the filter, with the tradeoff that you lose the view of the nice starfield next to the tarantula.
The view of NGC246 was substantially improved with the filter, giving more contrast and showing more detail than what could be seen without the filter. It gave an almost 3D appearance to the circular looking planetary. I'm very happy with mine, for AU$80 to my door. The 2" version is obviously more expensive, but still significantly cheaper than the upmarket alternatives (astronomik/lumicon etc).
As others have said, you don't need the filter to see the nebula, but when used, it can enhance areas that you can't see visually, as well as increase contrast to give a different view of what you could see before.
Filters will sometimes give you false colour, making things look greenish or blueish, depending on the filter.
HTH
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