Delos is possibly the best eyepiece TeleVue have ever made. Being a new generation eyepiece they out perform the Nagler in every way, except for the difference in the field of view, and the type sixes have a smaller form factor if that is important to you.
If you consider you could use this eyepiece for the next ten or twenty years I wouldn't think the extra $40 cost of the Delos would be a factor. Those extra dollars buy widefield optical excellence. Personally I think the 10 Delos is a no brainer and would work wonderfully in your Dob or any future telescope you may own.
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