<p>If HM is your definite first choice, and if you don’t care about comparing offers, and if you just want to know if you can afford it, applying ED is fine, and possibly confers a slight admissions advantage. If the offer is insufficient (and you don’t have to decide until you receive it), backing out is easy; here’s the Common Application rule:
You say thanks but no thanks, and apply elsewhere RD, but have those apps ready to go by the time (or before if necessary) HM sends their decision. You would withdraw the other apps when you accept HM’s offer.</p>