I got one of those to try it out and they are kind of unwieldy design. Short, stiff cables. Everything needs to sit just so and if you touch it, can easily become disconnected. Especially if you get the kind with a second USB for power. You need to get a ?charger? (therefor a dedicated electrical outlet) for each drive.
I'm not sure, but I think even though the USB hub is powered, the bigger ones need extra juice. I don't believe they can be solely powered through the data USB connection. Could be wrong.
Do you mean the ones that are sold as drive duplicators? Those were the most affordable per HD of what I found. I don't really want to have a button that would erase or write over my drive though. That's asking for trouble. A couple of reviews I read mentioned that the particular devices were really aggressive about power management, and would turn themselves off after 10s or 30s idle. Which sounds very annoying but makes sense if the main thing is to clone drive-to-drive. Not sure if they're all like that.
Anything? Some of my "portable" type HDDs don't have external power input. So there must be some situations in which it is feasible?