If you have a digital camera sensitive to UV light, this filter really works. In contrast, most so-called "UV filters" don't block enough UV light to make a difference in your photos.
This filter eliminates purple fringing when used on my Olympus Micro Four Thirds cameras. This is the filter to get if you hate purple fringing and you think that the tools available to correct it in Lightroom aren't as good as eliminating the problem at the source.
Tiffen appears to make perfectly fine high-quality uncoated filters. I can't see paying six times the price for a B+W filter that does the same thing. As long as the sun isn't shining on the filter, I can't detect any loss of image quality with this filter on the camera.
On the other hand, because it's uncoated, if the sun is outside the frame but nevertheless shining on the filter, it causes pretty massive ghosting. However, there's no company making a coated version of this type of filter, so this is the best you're going to get, and at a bargain price.
I don't recommend using this filter under artificial lighting, because artificial lights don't give off much UV, therefore this filter can't help your image quality under those circumstances, it can only hurt it.
It's too bad Tiffen doesn't make these in smaller sizes for mirrorless cameras. I need to use a step-up ring with the 52mm size.
UPDATE: Unfortunately, I have seen other instances where this filter caused significant ghosting besides the obvious shooting into the sun. Such as shooting from a dark street into the light on a cloudy overcast day. So the lesson I learned is that one can't assume that this filter will always improve outdoor photos.