This mattress topper was very comfortable, and there no smell. I ordered the full size and my regular full size sheets still fit the bed with a standard mattress and the 3" topper. 
Unfortunately, it retained way too much body heat and I woke up sweating most mornings (and I'm normally pretty cold without a heating pad of some sort). 
I also didn't account for how 3" would change the view of my laptop on my desk from my bed, which made the end of the bed higher than the screen so I had to prop the laptop on some books to see it. It was also awkward reaching the cubie hole on my bed side table once the bed was 3" higher.