How good is 3. Bb5 Closed Sicilian?

While working on my repertoire for black I've stumbled upon this interesting variation that white can play. It is quite unpopular (about 16% of all the Closed Sicilian games in the 2000-2500+ rating range) and I found it very interesting. The position is equal after:

but almost any position after it is very rich, having a great amount of options on any move for both sides. The question is: does anybody have experience in this line and what was it? How good is it practically?

A recent book by Robert Ris on the Anti-Sicilians gives a suggestion of 4...e6, so not sure how common 4...a6 would be. The engine does show 4...a6 as best, but I'm not sure as black why I'd want to force the bishop away from the b5 square.

I play the Bb5 Sicilian as white, but begin with 2. Nf3 specifically to avoid that position. On the white side of the board, I generally try to force the exchange of bishop for knight to either cause doubled pawns or fight for d4 supported by c3 in the absence of black's c6 knight. The white bishop is usually otherwise homeless, with the exception of a few lines where black delays the a6 "kick" and white has time to castle and move the rook to e1 supporting the e-pawn and creating a little pocket on f1 for the bishop. Given all these efforts to re-home or trade off the bishop, I think your defensive move of Nd4 is quite a good idea. If white starts with the closed Sicilian (2. Nf3), then the c-pawn is blocked and white doesn't have the cute option of hiding the bishop on c2 behind the pawn wall, like in the Ruy Lopez. I'm curious what players of the closed Sicilian have to say, maybe other people have clever ideas!

I play the Sicilian as Black, this is a pretty decent line, it's harmless if you remember the theory, but it's difficult to do that as it comes up so rarely.

Totally different openings.

Because you want to prepare ...b5, this is a normal expansion in the Sicilian, and because White doesn't have a good alternative square for the bishop. c4 turns out not to work well, so White has to go to d3.

I love to play as black in this postion i havent faced Bb5 that much but whenever i face this i played Ne5 and won 5 games out of 5. Like it is very corfortable to play as black if you know the theory the position you get is like very good for black .Like black get lot of counterplay in this opening with b5

It's good enough to be played in a match for the world championship. Caruana played it repeatedly against Carlsen in 2018.

No, that was the Rossolimo, where White plays 2. Nf3 rather than 2. Nc3, the two lines have nothing in common. The Bb5 Closed Sicilian is a pretty good line at club level, but I don't think we will be seeing it in the world championship anytime soon.