So as of right now, are there any real advantages of purchasing the RZ as opposed to the SZ which has the ability to be used with both Rekordbox DJ and Serato?

They are both pretty close in build and layout, the RZ has some updates to the controls:

• sequencer
• quantize
• capture
• sampler quantize / sync

I can't be sure if other changes were made to the internals.

Also the microphones were upgraded in input level for mic 1 and unbalanced to balanced for mic 2.