Not to say I'm an Anovos fanboy but Anovos is the only mfg given access movie costumes, though the OTTK is still up for debate lol. Their accuracy in many aspects will be very close. Disney and Lucas have very strict guidelines they need to follow so again you can trust it will be very close to canon.
That being said I have the FOTK beta fiberglass helmet. From what I understand all the fiberglass helmets they make weigh almost the same, within 1lb of each other. My FOTK was roughly 5lbs. Being the DT helmet is a large construction hemet with greeblies I say is will be close if not heavier than others. Without having one in my hands that's my educated guess.