I agree. I run the Ameriglo GL-429 (aka XL) with the RMR and the GL-470 (aka 2XL) with the SRO. However, the DPP deck height is significantly taller than the RMR, so he'll need the Ameriglo 8XL or 9XL set that I linked to above if he opts for a set of serrated black sights.
If he is worried about front sight visibility as he is just starting to use a red dot, a white sharpie can be used to put a streak of white on the front sight. Later on it can be removed with a dab of alcohol once he is more comfortable with red dot sight acquisition.