What's wrong with something like this? (I think about purchasing one)
Nothing as long as you are running on 240V and all your rigs combined used less than 2.4KW.
There is also nothing wrong with the PDU that giga linked to. Switched PDUs rock. I was so glad in my last job when our company stopped being cheap and upgraded to switched PDUs. Click-click reboot crashed server. Their only downside is the cost per watt is pretty high as they tend to be designed for dense racks, so they have more ports and less wattage than we need.
If I could find a switched PDU that had:
* 30A input (24A usable) @ 240V
* NEMA L6-30P plug
* At least 6 C14 plugs
I wouldn't have even started this thread. I would have bought it last year. The only problem is .... it doesn't exist. I guess one way to look at it would be a new spec: "$ per KW switched".
The PDU giga linked to: 20@ at 240V = 4.8KW. $450 / 4.8KW = $93.75 per KW
The PDU you linked to: 10@ @ 240V = 2.4KW. $130 / 2.4KW = $54.15 per KW
The best used PDU I have found on ebay: 30@ 240V = 7.2KW. $600 / 7.2 KW = $83.33 per KW
USB board efficiency would depend on how many rigs and how much wattage:
USB relay board powering 6 1000W rigs. 6*1000 = 6.0KW. $100 / 6.0KW = $16.67 per KW
USB relay board powering 8 1200W rigs. 8*1200 = 9.6KW. $100 / 9.6KW = $10.41 per KW
Mini USB relay board powering 4 1000W rigs. 4*1000 = 4.0KW. $75 / 4.0KW = $18.75 per KW