Brnton Eterna 62mm vs Alpen 80 mm
After carrying the big stuff for many years for my birding, I got tired of carrying all that weight and went to a Kowa 663 (66mm ED objective). No, at 60x it was not QUITE as sharp as my old Leica Televid 77 APO or a Swarovski AT80 HD, but it was plenty sharp enough and much lighter. The Kowa has never failed me, even out on the shorebird mudflats for some extreme birding. No way will I go back to carrying a big scope over my shoulder all day. Then,too, carrying a smaller scope means you can get away with a lighter tripod and save even more weight. I say go for it.
Depends on how much you want to spend and how deluxe you want to go, but I have used a Nikon 848 tripod with my Kowa for years and it has never failed me. It is not the smoothest head, but, then, I am not using the head to pan with a camcorder and so on. If you want something a bit smoother, try a Bogen head, such as the 700RC head on top of a 190 leg set, such as the 700RC, 190XB, assuming it has enough height for you.
I haven't heard that it is discontinued, but when a Nikon product goes to backorder, there is sometimes a long delay in availability. Other similar tripods, though, in terms of quality and price, include the Bushnell 784040 and the Vortex Pro GT