Seat post rack for commuting help
 

I know everyone has been on pins and needles about what bike I should get. I stopped into an EMS and found a Kona unit on sale. Just what I want but no braze ons for a rack. What about seat post rack for hauling stuff to work? Do they work ok? How much can you carry? Do they move side to side? I love the price and it's a ss with disk brakes. The inability to use a regular rack is what makes me pause......any ideas?

What about this as a rear seat post rack-does it really allow you to use panniers?

Amazon.com : Bike Seat Post Mounted Rear Rack Commuter Carrier, fits 26", 700c, 27.5", and 29" bikes : Sports & Outdoors