No, there's no reason not to use egg substitutes, but when you're shopping, be sure to check the labels carefully to learn what the products actually contain. In most cases, you'll find that the primary ingredient is egg whites, which will give you lots of protein but no fat or cholesterol. However, some egg substitutes contain less desirable ingredients such as vegetable oil, cellulose gum for thickening and corn oil as a carrier for beta carotene and the fat-soluble vitamins. Check the calorie content, too. The substitutes can range from a low of about 15 calories per serving up to 60 (a whole egg has about 80 calories).
Some egg substitutes are fortified with the vitamins and minerals found in egg yolks, so you won't be losing out on any of the nutritional benefits of whole eggs (again, check the label to make sure an egg substitute is fortified with such nutrients as vitamins A, B-12, D and E, as well as other essential nutrients such as folic acid and riboflavin). Be sure to check the labels, too, for information about shelf-life. While unopened egg substitutes can last for about 90 days (compared to 60 days for whole eggs), once you open some of these products you have to use them within a week or throw them away.
While I see no harm in egg substitutes, they are costly compared to whole eggs. I think it is more economical to use whole eggs to get egg whites, even when you throw away the yolks. You can make a delicious omelet by combining two egg whites with one whole egg. In cooking, you can substitute two egg whites for one whole egg.
If you're trying to lower your cholesterol, I would focus on reducing your intake of dairy products and the saturated fats in red meats, rather than on your egg consumption. Remember that eggs can also be a vegetarian source of omega-3 fatty acids, especially if you buy specially fortified ones, which are becoming more available.