Thanks to all the FKK posters for the various leads and comments. I visited FKK Mainhattan in February and found it very accommodating and well-run, in general largely as described in the above post and elsewhere —though I'm not sure that I negotiated prices as well as I might have. I averaged 200 EUR per one-hour session with each of several girls during two visits.
Let me add that in addition to the 60 EUR entry fee, there is a 5 EUR charge for a terrycloth robe, which I would advise to anyone, even those with a David Beckham-type build. If nothing else, it's nice to have the option to cover up.
I can't say how representative my experience was, but given the time and money, I would go back in an instant. While it may not an experience for budget travelers, one might want to budget for the experience. And while he's been known to slip in a winking aside in re the 420 and girl-in-the-window scenes in Amsterdam, Rick Steves' brief reference to FKK clubs omits any mention of the real reason for visiting one.
And regarding the unlimited beverages and food included in the entry fee, only beer —of disappointing quality in light of the fact that this is Germany— and soft drinks qualify. There's an extra charge even for a glass of wine. Not surprisingly, thought, the bar can be one of the spots for an initial, low-pressure, get-acquainted meet with one of the ladies in addition to serving as a perch for observing the general scene.
The food, while not exactly the reason for attending FKK Mainhattan, is cafeteria-style but at least decent and regularly replenished. It could even send you back for seconds —thus perhaps calling for a little self-restraint at mealtime. The fare also includes fresh fruit: recommended both before and after most amorous activities.
And it's interesting that the customers and the girls all eat in the same room. I was struck by the degree of implicit respect by all for one another's private space in this communal space —and yet, though the ladies tend to eat in pairs or small groups, this could be another low-pressure venue for meeting a potential hook-up.
One question all Americans might be left asking, at least rhetorically, is, "Why in the h&ll don't we have anything like this back home?" p.s., Legal Nevada brothels don't count. It's much more than a matter of there being a place with X number of women instantly available for sex for a certain price.