I use it alone and it works great.
I use this product as a day moisturizer, alone. It leaves my skin with a finish similar to that of MUFE HD primer, but the 'moisturizer' effect lasts throughout the day , even with a matte foundation.
Depends on your skin type. This is a very light, non-greasy, gel-like lotion. If you have oily/combo skin, you can probably skip the moisturizer, but dryer skin needs a moisturizer on top.