I use a plain ol' kids glue stick. Always thought that fusible stuff was so expensive and I didn't like the stiffness.
Cut out your piece that you need to attach. Carry your glue stick around in your pocket for a while, works much better and wont stretch fabric when it worm and goes on easily. I just give the piece a little dab or little swipe of the glue stick and attach it to where I want it. Apply a little bit of pressuer an you are good to go! You can pick them up and reposition them for a good hour after being put down. Even when dry you can tug them off by the fabric may stretch out of shape.
I saw,ah, what's her name, Bonesteale(?) using them on an episode of her show on PBS. Once it dries, it doesn't gum up your needle either. Washing will remove it. It's all I use anymore.