From what I can see, the difference between the What The Sport Singlet II and the What The Sport Singlet is that the updated version has double shoulder straps and ruching on the upper back. The fit between the two is very similar. I also bought the same size this time, which is size 6. Here it is on me:
I really like the white contrast piping against the pink lemonade color. It just catches your eye and makes the tank look a little more special. I actually already wore this tank to workout in! I was very surprised by how well this color/fabric hides sweat. I had a pretty tough workout, and was definitely sweating. The tank, however, looked completely dry. But when I touched it, it was definitely damp in some areas. I'm not usually someone who gets embarrassed by sweat stains when I'm at the gym. In fact, a lot of times I judge how hard I worked out by the state of my tops and bras afterwards lol. So this is just something I noticed, and I think it could make a difference for some people.
I also bought a Lorna Jane tank on ebay for super cheap! It was like under $10 after shipping I think. I actually really like it! I don't know the name of it though, and I couldn't find it on image search. But it's a white cotton tank with sheer stripes throughout. It's a size S and it fits well. I could see it being worn casually or to workout in.
So the only thing I'm not crazy about is this pink "Lorna Jane" tag on the pocket. There's already a metal logo on the usual spot on the back, so this is pretty redundant. I think I'll see about cutting it off.
Well that's a minor detail, but I love everything else about this tank! So that makes me pretty happy that I got it for such a good price.