Not anymore... I sold my version 1 lens about a year ago. It performed well under bright conditions but in low-light, not so much. I understand that the version 2 one is considerably sharper than the older one, and does much better in low light conditions...
I have the mark 1 400mm f4 DO. I bought it from new but have hardly used it. Not because it is a bad lens in any way, but because I used my 500mm f4 most of the time.
I have it for sale on ebay at present. The images I took of it were excellent as you would expect from such a prime lens. The main advantage over the 500mm f4 is the versatility in terms of lightness and ability to hand hold it when doing flight (and other) photography.
I will be sorry to see it go but I need the cash for a new camera body.