I've been milling with the 56" forester bar with my 661 for over a year now. I think it has been a great value, and I even bought a second one recently to keep as a backup.
I will admit that it probably isn't as good as a GB or Canon, but it also doesn't cost nearly as much as either of those!
A couple of issues to keep in mind though. I've found some increased wear on the tail end of the bar where the chain hits right after the rim sprocket. I believe that is primarily due to low tension when the chain gets warm and stretches a bit in the cut - I've seen the chain lift off the bar when revving for subsequent cuts. I try to keep it tight, but with 168 drivers, a little bit of stretch multiplies very quickly. I do expect to wear through the bar eventually, which is why I went ahead and bought a spare, and I also have a spare tip that I keep on hand, just in case. I also used calipers on the groove, and found it a bit wider than .063 as compared to my other bars, but it didn't both me too much - I might get a bar squeezing tool and tighten it up a bit in the future if it causes me any problems.