In my experience, IR builds tolerance way too fast.
I agree that it would be nice to have IR for those times you want shorter bursts. But I ran into its shortcomings too quickly as a daily burner, not so different than trying to therapeutically bump cocaine.
There's also dirt cheap generic IR but there wasn't generic XR back then (still?).
* The XR release mechanism is unreliable - I've gotten lack of therapeutic effect, and "prescribed overdoses" from the 30mg ER.
* Proton pump inhibitors interfere with the XRs more than the IR.
* I can take a half dose if I don't want to be medicated all day.
* I can split and tune my dose around any other medications / activities i have going on (sports, cardio etc).