These "exam"-style interviews are innately suspect for the same reason they are useful: because they approximate real work very closely.
Look at how many malicious entities use spurious job postings to farm resumes and other kinds of data. You think there aren't unscrupulous companies out there extracting free labor from their "interviews"?
If the employer is very reputable, you might be able to feel safe undertaking this kind of interview. But when you are applying to a shady tech start-up (and they are all shady, and they're where most of the jobs are), there is no way to know whether the job actually exists.
Look at how many malicious entities use spurious job postings to farm resumes and other kinds of data. You think there aren't unscrupulous companies out there extracting free labor from their "interviews"?
If the employer is very reputable, you might be able to feel safe undertaking this kind of interview. But when you are applying to a shady tech start-up (and they are all shady, and they're where most of the jobs are), there is no way to know whether the job actually exists.