reti gambit accepted reverse cormorant gambit

You mean this?

Good catch, that's probably what OP meant.

I found Cormorant in scid_dot_eco file.

I think Reversed Cormorant 1 Nf3 d5 2 c4 dxc4 3 b3 is "good" if black takes 3 ... cxb3 4 Qxb3 because

• white gets one or two tempi for the pawn, call it one and a half;
• the sacrificed pawn is a wing pawn.

I think it's "bad" because

• need three tempi in the opening to fully compensate for a pawn;
• black didn't waste any time nor make any weaknesses accepting the pawn;
• a pawn is a pawn, black can now play to win in the endgame while white needs to make something happen in the middlegame.

But there is still a game of chess to be played after. Playing gambits, whether sound or dubious, teaches a lot about the pieces and how to play chess in general.

Black can decline the gambit as well.

This e5 idea is not new, for example 1 Nf3 d5 2 c4 dxc4 3 Na3 e5!? Tartakower - Spielmann 1925.

This is one way out of many to play the opening a pawn down for no compensation.