Yes they do work, however I do not know how much it inhibits the absorption. But something you said is a little startling;
"It seems harmless to me!"
Blocking the absorption of carbs is VERY dangerous especially depending on how much you are blocking. Carbohydrates are your bodies fundamental fuel/energy source. By messing around with the absorption of it, it can lead to a string of problems not to mention some very much unwanted bowl problems (high amounts of carbs in the bowel is what gives it it's smell). Your workouts will be terrible; you won't be able to do more than a light workout which in turn slows down your metabolism so your body isn't burning as much fuel/calories. You will find it hard to concentrate and your mood can change (similar to that of low carb diets) and I'm sure there will be more side effects I'm unaware of or haven't thought of at the moment.
If you are concerned about having too many carbs, just don't eat as many but please remember that carbohydrates are the number one fuel source and the ONLY fuel source of your central nervous system.
Do they work, yes, no, maybe, not really sure….it all depends on what you’re intent on achieving. Technically & medically they may work at blocking carbs, but they won’t support your goals in being & maintaining a healthier lifestyle.
Here’s the deal with concepts like this…..you’re going to pay a ton to be on it, you never know what the chemicals are really doing to your internal infrastructure REGARDLESS of the studies & research provided & if & when you do stop it & you reintroduce moderate & normal amounts of carbs….the weight will most likely come back & bring friends with. Keep in mind that is not a shot at low carb diets as I know plenty of folks who utilize them & have success in their own way with them, it’s just the concept I’m not a fan of.
At the end of the day, I wouldn’t aim for “get slim quick” tactics, but more or less implement a solid strategy with a clean diet, exercise & increased activity, R&R & keep doing what you’re doing & you will make progress.