Wow. I really had no problems. As I say, the screws came out with ease (using the right screwdriver of course).
As for breaking into the plastic seal, I used a plastic tool designed for that purpose (I used to change a lot of mobile phone cases and this tool came with some of the cases). As mentioned though, a credit card type would do just as good a job.
The hardest part is definitely, as mentioned, around the battery. Don’t force anything, just run the card along the seams and it’ll pop eventually.