I get your point and agree to an extent.
I actually voted for him to be our fullback cover whilst Tom's out.
I just think that if we were a settled squad ( when was the last time that happened? ) he would be ideal to cover and float through a few positions like you say but we're not.
Look at when Foz and DCE debuted, they came in, knew their role with the same team week in, week out and that's all they had to do.
Hopefully in the next few weeks we're settled enough that he can come in as a specialist 14 and tear opposition teams a new one.