It's easy, there are only a few things to keep in mind:
- Use lots of downwards pressure initially to "break the seal" on screws and avoid stripping them
- Do not overtighten the screws, a snug fit is better than tight
- The shells are cheap and often the plastics aren't molded properly (requiring minor modification) or easily strip when putting screws in
- Do not use any free screwdrivers that come with the kits, buy high quality ones
- Avoid myriann and rebranded copies of their goods
For what it's worth the dpads are not great on them and the texture is really slippy, but they do look great.