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The whole idea of a KDF is to use the output of the key material as, well, an unpredictable key to an attacker. So as long as your IKM is secure and preferably your salt is unique, then the output of a KDF should be usable as key.
For HMAC it is best to use the same key size as the output of the hash algorithm used, as per HMAC spec:
The key for HMAC can ...
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