In general I think the transition isn't too difficult, as mentioned above the toughest part of bringing the harp guitar to life is managing your sub-bass strings in terms of muting; too many strings active will generally sound very bad. Simpler songs (eg. Into the Ocean by Andy Mckee) that require less muting due to simpler bass melodies are very approachable
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The only other thing that could complicate learning the harp guitar would be ensuring you don't accidentally mute the bass strings when they need to be sustained. This will depend on where you anchor your right hand to your normal 6-string.
A veteran of the acoustic guitar could make the transition with relative ease, depending on experience i would think
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