After many tries I decided to pcie images not USB sticks
The cheap USBs don't work, many errors mostly IO Linux errors.
Need USB3 type thumbdrives for best results.
6 of my newer rigs Z170s mobo, no SSDs or m2, uses USB3 thumbdrives and runs well.
The other existing 24 rigs - do have SSDs already, I just replaced the Windows with smOS image.
If you have m2 storage, I think its best to use them because cost of small and cheap m2 storage still does its job at wire speed, versus a USB which will need USB3 for speed and decent capacity 16/32GB, which probably is around the price of the m2 storage and USBs if not from reputable brands, have many horror stories usually manufactured in small dark alleys.
I got screwed on some sandisk usb 3.0 sticks they did not work well.
I saw the lot of 10 m2 pcie ssds from kingston 48 bucks only $4.80 a pcie they are gold so far
http://www.ebay.com/itm/112143250197?
very good buy this Phil.
m2 storage will be really fast and Linux will love that.
USBs are designed for data/files portability -- so -- its best to go for reliable permanent storage at wire speed.