I got the impression that he is going to transfer the data off the current drive, that isn't RAID, to an external drive that isn't RAID either. If true, then RAID isn't an issue. I'm not a RAID expert, but I think that when using drives of different size, that it would set the RAID to the smaller drive size, but the RAID would work okay. The unused portion of the drive may not be accessible, but I'm not certain about that. If the RAID is set to mirror, rather than striping, I think that imaging and cloning would also work, because both drives have exactly the same data on them, where with striping it is scattered in a fragmentary fashion across both drives.
If I recall, the version provided by Seagate is the lite version, which doesn't have many of the features of the retail version. This shows a comparison:
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But I didn't see whether it includes cloning or not.