it depends. in some you may see on MRI an interaction of the oral tongue with the palate and also gain a more global view of what happens in the entire pharynx at any point in time. In DISE, you may wish to consider also doing an oral endoscopy to observe what the tongue is doing.

I agree with Ofer Jacobowitz, Sleep MRI has the advantage of the global view of the upper airway plus being able to identify the thickness of the lingual tonsils, so it can help you to choose a surgical technique. But as is really complicated to perform it during natural sleep, the disadvantage of sedation is there....

I don't know if it can be cost effective compared with DISE. I guess that it depends on your hospital....