In SALESORDER_CREATEFROMDAT202 Basic type you have E1BPPAREX segment which is same as EXTENTIONIN as in BAPI.
Again in general term Call Transaction Vs BAPI. BAPI is any day preferable . And it is also easy to update custom fields via the BAPI than using exit in IDOC_INPUT_ORDERS.
But again in consulting world, ORDERS is widely used, so the middleware developers also are accustomed to the mapping technique and ORDERS Idoc gives the flexibility to use the cross referencing techniques like EDPAR/EDSDC by Standard which BAPI won't give by default. So in true EDI (EDIFACT/X12/TRADACOMM) Scenario I would go for ORDERS.
Now you can take a call I guess 
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