I bought this program almost as soon as I saw it, and it's OK, but I wouldn't say that it's great.
First off, it leaves a fairly obvious footprint since it runs based on a catchall and doesn't have a randomization option for the timing on the stumbles. It's fairly easy to see that the same article is stumbled every 5 minutes exactly, by people who all registered with emails from the same provider, and I think that impacts the traffic.
As for the traffic, mine has been tailing off. I got a lot more right after the release of the program. Sure, you get a few visitors from the stumbles, but not as much as what I've seen from doing stumbles manually from multiple accounts.
With that said, yes it does generate some traffic for you, and it works very well overall. The friend adder is a little confusing but it works well enough. Nova has also been very good about releasing updates.
It's the best bot for stumbleupon I've seen, but it's far from perfect. Take it for what it's worth.