The new syntax is better, and others may disagree, but I'm not convinved worth keeping backward compatibility with old form. After all the name of the program changed not so long ago from 'regress' to 'ecl-test'.

Besides, I think it should at least check to see if the new form --cluster has been provided,
e.g.:
> ecl-test query --cluster thor a.ecl b.ecl c_ecl

should only need to detect e_ecl as an invalid query, not an invalid cluster.

As I say, I'd drop the old syntax in favour of the unambiguous new one.