macmac,
I thought I knew but I wasn't certain so I looked up Tesla Effect at Amazon and checked the customer reviews since I doubted Amazon would make the answer to your question plain.
Out to the right in the "more recent customer reviews", there is one headed "good game...but BE WARY of Amazon's direction for loading this game" by bricescreek.
All the way at the bottom of his remarks he mentions Steam.
So there's your answer.
You're buying a Steam code.
If you use Steam, that may not be an issue.
However, I notice that you have a SE Asia location in your mini-profile at the left.
Amazon notes that: Currently, this item is available only to customers located in the United States and who have a U.S. billing address.
Just an FYI, in case it will affect your buying the game from them.
If you want a direct download without needing to go through Steam, you can get the game from GOG.
And if you're patient and watch the flash sales which come up every two hours until June 30th, Tesla came up before and probably will again at 25% off the list price of $19.99.
Edit: GOG sales are world-wide so you shouldn't find Amazon's US limitation on buying the game.
Gil.