While the basic idea for the Mesh Extenders is having seamless roaming and using the same SSID, certainly the more basic like the EX2700 [2.4GHz only] and AFAIK all Netgear Wireless Extenders allow configuring different SSIDs (network names) for the access points for each band.
This does not make the two networks dedicated subnetworks, it's all L2 bridged (or L2-MAC-NATed for the simple units).
