Works for me, but like any filter it's easily overused if you're not careful.
I used to use Niks filters a lot when I wasn't such a good photographer, they are good at giving a boost to an otherwise dull photo, but then as you progress with photography you start to realise just how amateur a route it is and that you should shoot right in the first place and then apply individual processing to that image.
A lot depends what you want to achieve, sometimes a filter can save you hours of processing... a daguerreotype effect for example. Not necessarily Nik, there are loads. I can understand the purist viewpoint, and thats great for you, in business, time is money, and if the customer is happy, that's all that counts. If you can do 10 in a day instead of one, thats great for the ole pocket. For those without thousands to spend on expensive lenses, you can emulate the characteristics of one using layer masks... and filters. Again, less is more, don't overdo it. Filters have their place, just don't overdo it. another filter would for example be the raw output sharpener. filters are easily dissed, mostly by those who run them at 100%.
When you do frequency seps, guess what, ya, it's a high pass filter.
Noise reduction function, yup, it's a filter...
Some of the Nik ones are amazing, others, not so much, on their own, but in combination with other NJik, or other companies filters - you can do some really clever stuff. Try doing a droste effect without the filter for that one. Its good to be purist, but nobody should discount the possibilities on offer for creativity atop a base photograph.
I rest my case m'lud.