Mine has proven to be well work the premium cost (about 3x the price of a conventional bucket). But I can't really go along with the bulldozer comparison. As far as pushing dirt, I'd be more inclined to consider it a light duty scraper - but one that is pushed rather than pulled. For example, I have teeth on my bucket edge, which make for a rather sloppy scraping edge. So I open the 4in1 and scrape with the inner edge. The forward motion pushes the dirt rearward. So when I can see from the cab that the back half of the bucket is full of dirt, I close the clamshell on in.
It got a good workout on a pile of rip-rap yesterday. I used the bucket teeth to break into the pile, something that's hard to do with a scraping edge. But by the time the pile was gone, the earth beneath it was pretty torn up. I then opened the clamshell, and cleaned it up by scraping the high spots and back-dragging the fill back into the low spots. In the past, I'd have had to do that with my box blade and landscape rake.
As far as picking up logs, it takes practice. I'm lucky the John Deere has a sloping nose, cuz it's hard to see what the clamshell is doing so close to the front tires. Assuming your 6040 has the same or more slope to the nose, it shouldn't take you too long to become proficient. I also use it to grab broken but dangling limbs off trees (ice damage) and pull them down. Before I had to get up and down off the tractor several times with a chain while pulling them down and dragging them off.
One shortcoming (compared to a regular bucket) is that they can't carry water. Nevertheless, I still wouldn't be without mine
//greg//