I brought out my F4 just to have a look, as I cannot remember ever having had (or, more precisely - ever having realized I had) that issue.

With my eye as close to the (DP20) finder as possible, I found I could still see both displays clearly - however, either one will be in my peripheral vision at any time; I cannot read both without moving my eye up/down a bit.

As for a DW20, I see KEH has got one in excellent condition for well south of US$100. (It is a most useful accessory; I use mine all the time when I do still lifes or macro - it makes life a lot easier.)