An alternative hashing method, how does it compare?
Isn't the second method reducing the hash's target space because it is only 2 x 'chunk size' (which is less than the original size if number of chunks > 2)? If the target hash space is smaller then collisions are likely to be higher and the resulting hash use is therefore weaker on that basis (although this isn't the most important factor with reasonable size target spaces).

Obviously this is a simplistic analysis comment and not a full crypto analysis - for that you need to have a solid grounding in cryptography mathematics.