For the pink ones, I've followed the instruction to interface all top and heel portions but perhaps my fabric used was abit thick, so it came up to be tad too stiff. Decided to do away with the interfacing for the green shoes and it came out just nice with some body but not too stiff. So my advice to those of you who are trying, to use interfacing only if you fabric is thin or light weight.
Anyway, it's very easy and nice project. Oh, remember to press the seam and folds as it really helps when you need to fold over and it gives a neat feel to the shoes. I'm thinking about making some more shoes and bibs to give away with them.
Go on and try it if you haven't. It's nice and easy and you can sew up 2 shoes in 1 hour.