I can’t recommend the microwave. If the the iOpener becomes too hot, it bursts. Better put the opener in cooking water. Dry it and use it. Instead of an iOpener you can use hot/cool packs as well.
I used the kit from iFixit. It worked fine. But I killed the iOpener in my microwave. So I had to replace it by a cooling pad. This works as well. I would not recommend to heat it in the microwave. Heat the iOpener in boiling water. That way it gets as hot as it could, without overheating. Don't be afraid of water on the heated pad. Dry it on a towel after heating, but water on it evaporates fast, if it is really hot.
Step 31: Have a closer look on the digitiser ribbon. It is folded. When reassembling with replacement kit, fold its ribbon first. And it might be a good idea to remove the screen ribbon. It is attached to the board with a small bracket on the connector.
Before you remove the protection ribbons from the assembly kit, check whether it fits. In my case the screen broke as it fell on one of the edges. I had to bend it a little bit outwards so the new panel fetched in.
Have some spectacles cloth available for cleaning the screen if it might become necessary. Beware of dust