The AF-160 and similar ring flashes sold for Pentax are intended for macro and product photography use. Generally they are too puny for portraits. The larger ring flashes like the Alien Bees are what one uses for portraits.
That said, I've had some fun with my Sigma ring flash and people's faces. But the effects are not for everyone.
Here's one of my daughter:
Those ring light adapters for an external flash can work quite well for portrait work. Ray Flash is one brand that is considered good, but AFAIK they only fit Canon and NIkon flashguns. Strobist tested a couple of these a year or two ago, so do some research there.
Hope this helps.
M