Purely cosmetic, entirely trade enabled for both keys and crates, and you can preview the potential items of a crate to know if you even care enough to spend the $1.49. This is honestly pretty okay. You can draw a comparison to Overwatch, but Overwatch is way more scummy with completely random boxes regardless of whether you spend or not. But hey, at least you get some crap amount of coins for duplicates, right?
I'd take this Rocket League system any day, and at least they are being up front about what they hope to gain from the venture. All of you overreacting likely at most casually played the game anyways. They are aiming for the serious players, the competitive, and those that want to support their preferred e-sport but may not know how. For the cosmetic, totally optional stuff, (reasonably) charge away.
It isn't as if you have to spend money to compete at the same level as everyone else. I mean, ffs guys, you'd think Psyonix was holding a gun to your head demanding you buy these if you want to be on even footing in the game. When did everybody get so annoyingly offended by totally optional, entirely cosmetic, paid DLC? Not everything in life is a handout, and paid cosmetic DLC is hardly anything new. I'm sure when you have to choose between that McChicken and a key for a crate, your world will simply come crashing down.