Remember that "worth" or value is subjective and different for each individual. Generally, deciding if a particular eyepiece is "worth" the asking price is very dependent on how badly someone "wants" that eyepiece when factoring in the bank account balance. For those who keep $25,000 in their astronomy account, an $800 eyepiece doesn't present much of a challenge. And, there are those who "want" something enough to just buy it; foregoing other possible expenses. But most of us do have limits. I have been fortunate to own many eyepieces, some old, some new, some presenting wide and some narrow fields, some that were down right cheap for what they gave back and some that were absurdly expensive. I enjoy trying eyepieces and have learned much from the experience. I will not own ZAO I or II's again; nor will I buy RKE's again. But I enjoyed using both. They were both "worth" the price of admission in their own way.
I have found that rating eyepieces is very difficult for me, especially since most eyepieces perform differently in different types of telescopes. The older my eyes get, the more difficult it becomes for me to assess differences, and on-axis, the differences in many eyepieces are very subtle anyway. Companies like TeleVue and Pentax have shown that wide-field eyepieces can be used very successfully for planetary viewing. So although some observers find issue with multi-element eyepieces with a broad FOV, others find them perfect for their style of observing.
What I have found is that some eyepieces do perform better at certain tasks, so I do own a variety of designs that seem to complement one another. But to say that Delos is better than XW's or orthos are better than Plossls, you must see for yourself, with your eyes through your telescope, under the skies where YOU observe. Even then, you will find that one may perform best on one target while the other performs best on a different target. These are subjective tests with a multitude of variables. It's hard to correlate test data when you change the variables.
I think we live in a time that would draw envy from astronomers before us. We have lots of choices. So, Cathexis, go for the gold. If you want the wide field views of the XW, Delos or Ethos, go for it. If you are willing to accept the narrow FOV, go for the Tak or UO HD, both of which are very good and can be purchased new. If you are willing to wait to buy used, find a 6mm Pentax ortho, a ZAO or a TMB Supermonocentric. Each of them presents differently, but each of them presents splendidly.
One last note that you might find helpful... maybe not! Last year, I was searching for the best 6mm planetary eyepiece I could find. It is my most used focal length for lunar & planetary observing through my scope. I purchased and compared 5 eyepieces:
ZAO I (used)
ZAO II (used)
TMB SMC (used)
Ethos (new)
UO HD (new)
I used these eyepieces for about 3 months and did so when conditions were poor, good and great. In the end, I sold both ZAO's and the TMB... not because they did not perform; but because the Ethos and UO HD gave me something different that I liked better. I did find that on nights of poor to average seeing, there was simply no discernible difference between an $850 ZAO and a $100 UO HD. When conditions improved (maybe 15% of the nights), I saw subtle differences in contrast and scatter, but almost no difference in on-axis sharpness. YMMV, but my selection was based on what pleased me. I just recently sold the UO HD and purchased a Pentax Ortho which I do prefer. I mostly use a medium size (140) apo refractor and Zeiss prism diagonal... my choice might have been different though with a different scope or even with a different diagonal. I think the TMB SMC might be the king of scatter control (I own 3 of them now) so they are the best for me when looking at close doubles with a magnitude difference... but they present their image through a very narrow FOV, so I much prefer the Ethos for extended targets and for locating targets with their enormous FOV. If the seeing is average or below, I always use the Ethos. On those few nights a year when I can actually see a difference, I use the Pentax orthos and TMB SMC's.
Good luck. Finding the right eyepiece to fit your needs can be a delightful challenge.
Edited by GeezerGazer, 18 May 2015 - 02:19 AM.
