I don't think they're good for weight loss;
This isn't based on any exact sciences or anything of the sort, but I regularly see fellow hikers touting it as a lightweight source of calories while out hiking. They've got a fair bit of carbs (and quite often fats, dependent on the brand) in them and are quite light, hence their utility. Obvs eaten with something else like peanut butter or maybe a dry jam, but you get the picture.
If you want to lose weight you need to eat less than the recommended amount (calorically) and should probably just think about your diet a bit more than switch to eating cream crackers.