I have an ED50 with the straight eyepiece, 16x digiscope eyepiece, and the 13-30x zoom (the one that's used the most). What I have found is that with most all the spotting scopes I have owned/tested, a 2mm exit pupil is about as low as I want to go. This means 25x max with the 50mm Nikon. I also have a general rule about magnification... 1x for every hundred yards (i.e. you should be able to spot and get a "decent" view of a buck at 100 yards with your naked eye... at 200 yards, you need 2x... at 1000 yards you need 10x... etc.). Of course, this is just a ballpark estimate. More magnification would be even better if the image quality remains good.
So the ED50 gives me a good image up to 25x. I think 25x is good to 2500 yards. Again, this is my ballpark way of thinking about scopes and their application. This seems to work fairly well in the field too. Based on this, I feel that the ED50 is a great scope to "carry", but if you want to spot bedded bucks at 2 miles, this is not the right scope. At 2 miles, 25x is not good enough. 2 miles might seem far to some, but it depends on where you hunt. Atmospheric conditions will come into play at these distances too. And, if its dawn or dusk, a 2mm exit pupil is too small.
Whether the ED50 is good for you depends on how you plan to use it. I would suggest thinking about how far you want to be able to use the scope, and think about the exit pupil, objective size, and magnification like I described to figure out what size scope you will need. And then, think about whether you want to carry that scope!