I don't think "it is a bit overkill for what's needed in a playback deck" because, compare to other camera mounted (field) recorder, it is really cheap.
Please check the following comparison chart made by AbelCine.
http://blog.abelcine.com/wp-content/uploads/2011/05/Recorder_Comparison_Chart_051611.pdf
The cheapest uncompressed deck except BlackMagic Hyperdeck is Conversion Gemini ($6,295). Personally I think ProRes HQ 422 or LT is fine for playback but If I can get a uncompressed QT recorder, why not. People buy compressed Qt file recorder because they cannot afford CODEX, S2 or even Cinedeck (uncompressed QT is even option for this $9K recorder).
I see the ways to use this recorder and it is really fantastic option for its price.
Case 1: Use with Alexa.
Connect a Hyperdeck to Alexa's REC OUT A or B HD-SDI Connector and record Uncompressed 422 1.5G YCbCr. It is probably a better quality option than Alexa's SxS Pro Card recorder which only records ProRes QT. However, you cannot record ARRIRAW since it requires HD-SDI Dual Link connection.
Case 2: Use with Sony F3
Connect a Hyperdeck to F3's HD-SDI out connector and Record Uncompressed 422 QT which has a much better quality than it's MPEC-2 MP@HL (35Mbps/VBR).
The only problem I see from the above two cases is the editor may beg you to give your uncompressed QT to them instead of you begging them footages to edit your reel.