It just happened that I know someone in my hometown who plays the crab. He doesn't play in FIDE rated tournaments because of the cost of going to one and the fee; his national rating is about the same of his other countrymen who are rated around 2000+ elo.
My first impression of him was obvious as soon as I saw him unleash the "crab". He doesn't know what the opening is called but he calls it "Serangan sereng" or Side-swipes. (serangan=attack (swipes sounds better, sereng=side). He knows he wouldn't be able to castle but sets up a fortress in the middle, and to rip it open, unless prepared properly, would require boldness to let go of material, and also he's used to defending it.
If the other guy hesitates to rip open the center, he'd proceed building pressure on either side of the opponent's open files whichever side his pawn advance weakens the most. And it was also dangerous to those unprepared for it, especially when they've castled.
Whenever anybody draws in a balanced endgame position still full of life, he'd spring up and challenges everyone to take on one side and he'd play it to conclusion. Players loved to gather and watch him demonstrate converting theoretical advantages in the endgame, and once I, a brash kid then, openly pointed out a move I thought he played wrongly, only to be given an endgame lesson (I missed a couple of intermezzos).
In my opinion, below master level, the crab is as sound as any other opening.