(b) That's right. This question involves performance and breach of contract; and remedies for breach of contract.
Substantial performance is less than complete performance. However, it is performance that comes so close to complete performance that, despite the breach, the promisee still gets the intended benefit of the contract. In such cases, even though the breach is a breach of condition, the promisee must treat it as if it were only a breach of warranty. See Hoenig v Isaacs.
Accordingly, it is true to say that the performance cannot be rejected (or stopped) but the promise can claim compensatory damages to the extent that the breach has caused loss.