Count me a dinosaur! I still have and heavily use both the 20mm Nagler T2 and the 7mm Nagler T1. I also still have the 13mm Nagler T1, although I generally use my new 10mm Ethos instead as they yield about the same FOV. My son will get the 13mm T1 soon enough. OK, comments about the 20mm T2:
--(1) very sharp edge to edge with a Paracorr 2 and an f/4.3 Dobsonian. Equally sharp too with my other scopes of longer f/ratio,
--(2) there are certain objects that are best framed with the 20mm T2. However, I now use a 30mm ES 82 for centering objects in the FOV, then generally change right to the 10mm Ethos,
--(3) the throughput of the 20mm T2 is less than the more modern TV eyepieces. Therefore, I will use higher power eyepieces--which also by virtue of their higher powers produce darker fields--for, say, galaxy hunting from my Bortle 6-7 backyard, and
--(4) yeah, the 20mm T2 is heavy. Luckily, so too are the rest of my eyepieces, if need be with the brass adapter that TV sells.
For years, the most used EP in my box was actually the 13mm T1, though. Yes, it kidney beans. Yes, I learned to hold my eye so this wasn't a problem. I think it is still a great and underrated eyepiece. However, the 10mm Ethos is a masterwork. Oh, and the 7mm T1 is also fantastic eyepiece and I have no plans to ever replace it. Maybe Ole Al's greatest competition is himself?
Happy observing always,