Nighthawk M1 Unlocked Mobile Router

If I buy an unlocked mobile hotspot, do I just add a line with my current Sprint/T-Mobile carrier and use that SIM card for hotspot data use? I'm skeptical and am considering switching my phone carrier to AT&T just to reduce issues with having this hotspot. My question is: Will the unlocked + Sprint be just as strong, or does using the AT&T version make a big difference in quality?