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The main diference is that you cannot choose task - only check_primers is avaliable (which is obvious, because you need to provide at least some primers to have a result). RTPCR Primer Design and Posterior Actions tabs are also disabled, as far as their executions expect target sequences. After performing the calculation, you will get the result sequence with your input primers:
Result primers have the same qualifiesr as in a regular Primer3 calculation.