I find the counterbalance system in the 501HDV intriguing. Not having used counterbalance before I am not clear on what the experience of 5.5 lbs of counterbalance will be. With any luck counterbalance will eliminate or minimize the dreaded "tail dive" I have sometimes experienced with the 25x100s.
That's exactly what the counterbalance does for pointed up binos - it counterbalances the torque to keep the bino positioned in the altitude. The 501HDV has adjustable friction in both alt/az that can assist the counterbalance. With my setup, I feel I need to forward balance it slightly in skyviewing mode to keep the alt tension reasonable. You can also squeeze out some more tension from slightly locking instead of fully locking in the alt.
I track every satellite I see so I need good balance between the alt and az panning friction. I set the alt first then adjust the az to balance.
Truly depends on the weight and whether you are pointed mostly up or mostly horizontal. I use the 501HDV for 50, 70, and 100mm. You can shut the counterbalance off, which is great!. For the 50s, even at max alt friction, it still tries to right itself, so I turn it off. With the 70s, at a reasonable tension, it tries to right itself near 80-85 degrees - which is fine for me becuase I don't find straight up comfortable. Mostly horizontal with the 70s is fine with or without counterbalance.
The 502AH does not let you shut off the counterbalance - which is terrible for the lighter binos. If you're not in that sweet spot of balance vs. friction, you have to lock and unlock to pan and it gets annoying.
The 504HD would be fantastic and absolutely worth the money - if only it came with a flat base. You need to add an adapter to turn the ball head into a flat head so it just adds weight for no good reason. With more counterbalance settings, you can get a friction setting more to your liking.
The N12 is pricey so I didn't try it so that I can't know what I would be missing. But the specs give a pretty good idea that it can handle binocular telescopes and most refractors with ease. The 8lb minimum counterbalance also means no 50s or 70s without annoying.