P.M.
The long-term, maintenance stage is remarkably close to the way I've learned to eat now that I'm officially a "senior" and diabetic. I gained almost 50 lbs. over several years following menopause, which can do terrible things to women's metabolisms. I lost close to 30 lbs 4 years ago using the Atkins approach (but using everyday grocery purchases instead of expensive "plan" foods).
The Dukan diet does appear to be very similar. And I've had success keeping the weight off; in fact (and this could be related to my age), it's actually become easy to maintain, and in the past 2 months, I've lost an additional 6 lbs almost without trying.
But Wickerparkgirl doesn't express the whole Atkins diet correctly; it's not "eating just protein," but it does encourage increasing protein foods AND fiber AND healthy fats AND complex carbohydrates to significantly slow the absorption of meals in the digestive tract. Many people I know use "atkins" as an excuse to eat all the steak and bacon they want, and skip the vegetables. This is a gross misinterpretation of what the diet is trying to accomplish.
I suspect that if you really pay attention to the diet's intention, which is to cut back on low-quality carbs while balancing the rest of your foods carefully, you'll have success in the short run. And the long-term IS DOABLE – I seldom feel deprived on the 5-6 small, balanced meals a day that I enjoy now. And it hasn't been extra work or expense – I usually cook enough for a meal that I can have small servings of leftovers for a couple of days afterward.
Whatever approach you try, I wish you dazzing success.