I'd recommend staying away from Speed Download at the moment. It has never worked well with "cyberlockers" and their customer service is dismal. It does not work well with Safari 5.1. However, if you go to their site, there is no acknowledgement of this. They acknowledge it at the bottom of a single post (dated 2009 and intermittently updated) in the forums, which says that the problem applies to only a few sites. In fact, the problem applies to most sites. Should you do a web search once you find out that SD doesn't work, you won't find the results of questions and complaints on their forums, because they've gone through and deleted all of them. Not surprisingly, though, since they denied the problem for quite some time to customers. Of course, they've locked the SD forums too!
Oh, and the other thing, is that it appears they have a new version of SD in the pipeline. Wonder how much they're going to want for it?
Yazsoft has a pretty poor record. The screwed over the Mac Heist community a few years ago and were pretty unapologetic about it.
sigh. I've been have a spate of bad luck lately with small developers. It's a real shame. I don't know what's going on exactly. It seems like the App store is altering the market in a bad way. Everyone has to get their app up to whatever Apple's standard is and I guess it takes a lot more time and energy than some developers can handle.