BK12 & BF12 bearings

I am just finishing off sourcing all the parts for my first attempt at a gantry style CNC Router. I have 16mm ballscrews and open linear bearings on 16mm rod. Nema 23's drivers and other bits are coming from Zapp. One of the last items I need are the ballscrew support bearings. I have been surprised at the variation in cost (and its magnitude) of the BK12 and BF12.
Zapps price is not bad for a UK supplier but for the 4 pairs I need will still be £324+delivery but I have seen the following on ebay from China for £150 for 4 pairs including delivery.
http://cgi.ebay.co.uk/ws/eBayISAPI.d...=STRK:MEWAX:IT
Item number = 250525617620

Has anyone tried these. As a cautious person I thought I would check with the wealth of experience out there before I took the plunge.