1. Metering is done without the filter and no exposure compensation is needed. Increasing the exposure, for example, would reduce the filter effect and contradict the reason for using the filter in the first place.
2. I know of at least one photographer (me) who gets good results out of grad filters. My most used filter is a grad red which darkens skies, makes clouds "pop", but doesn't depress shadow detail in foreground textures.
3. The Chinese filters work fine in that they don't harm sharpness. What can't be predicted is the exact colour and density they send you. At times I've used two grad reds, one on top of the other, when I want more density than they supply.
For black and white photography with an experimental component these filters are an inexpensive entree into some very nice visual effects.