Simple Q&A D&D 3.5 (by RAW) XXIII

[Curmudgeon]

A 201 continuation

EDIT: I don't know if it bears any relevance to this situation, but the Kensai's very similar Withstand ability specifically highlights the interaction

Yes, this narrows the focus very well. Because the maneuver text lacks language similar to that in the Kensai class feature, you only get the stated ability: the option to make a Concentration check instead of a Reflex save. You get something that you can use in place of the save result, but both evasion and improved evasion require you to make a successful Reflex save. You cannot get the benefit of either ability if you simply substitute a successful result without actually making the required save.