I check the background before posting any international comp but it's not always easy to tell.
As for this:
1. There are over 10K of followers.
2. There is no sign of it being not.
3. If it were legit then it's worth a post coz of the prize; if it's not nothing is lost by just following/RT. Would I have posted this if it had asked for more details - probably not.
Is Nintendeal legit or what?