Why does this product no: CAI625 (ORSSOM OTR) require a tune when the Product no.: CAI621 (MACE/VCM OTR) not require one?

This ORRSOM OTR package requires a tune because the MAF signal characteristics are substantially different than standard, causing the engine light to come on due to the excessive long-term fuel trims required to correct the commanded air-fuel ratio. The MACE OTR package does not change the MAF characteristics to such a large degree as such long fuel trims are maintained within reasonable levels, resulting in the engine light not coming on.