They both do their job in lightening your other lip products, but there is a difference that Sleek is less then half the price.
In the pink packaging is Sleek Sheer Cover in Silk and the other is MAC Glaze lipstick in Bubbles which is from the Sugarsweet collection, they are both sheer formulas.
Now in the second photo they look exactly the same, but they actually aren't, whilst Silk is more of an Ivory golden toned white and Bubbles is a brighter pink toned white.
Top to Bottom Sleek Silk and MAC Bubbles.
I also did a swatch of a random lipstick to show how these lipsticks do their job
I used MAC Mattene lipstick in 40's Pink which a lovely medium rosebud pink.
Top to bottom
40's Pink on it's own, 40's Pink & Silk and 40's Pink & Bubbles.
My verdict is they're both lovely moisturising formulas, but obviously Sleek lipsticks don't have the Vanilla smell and I cannot detect any scent or flavour from this lipstick.