After playing with the units all day:
Out of 10: 8 work solidly @300 for 44 mh/s, 2 will not hash at all. Will keep plugging away at it before giving up.
I had one that I thought was dead, did not hash at all, two that hashed at 200 2 that hashed at 300, thats just trying the computer USB ports.
Plugged them into my expensive powered hub, all the suspect ones go and they all work at 400.
So some experimentation is required but I think some do need more power than others to go at full clock speed. Why the variance? who knows.
Im happy about the one that was dead initially, some decent power sorted it out. Also make sure you use both plug heads to give it the juice.
How hopeless is the power spec of normal USB ports ? Could be quite dismal it seems.
But to tell the truth I have a better experience with the product named after a lake and will go for those if I want more punch.