Two ZoneFlex R300 - Same SSID, Same Channel, will it boost the signal or extend the coverage?

You don't want to use the same channel, as that could cause co-channel interference, creating performance issues. Using the same ssid is perfectly ok and will not cause any performance issues. As for your question on extending coverage, yes two AP's mounted in different locations, not right near one another can add to the WLAN's performance capabilities..

Thanks for the reply.
My concern is that users have reported performance issues and drops.
I did some analysis and found that all devices are connecting to only one AP. The SSID for both APs are same and SmartChannel is selected and both are on different channels.
The other AP shows that "No stations are currently associated with this WLAN". How to merge them and use both their power as one?

Like Kevin said.  do not have them near each other (maybe at opposite ends of the warehouse) and have different channels.  I also have motorola scanners and they are not 5GHz capable, so you'll want to look at your air space with a wifi scanning tool and determine what channels to use.  I turned off smart channel on 2.4GHz cause it didn't work well for me.  I statically programmed them to 1, 6, 11 (I have 3), the recommended channels for 2.4GHz.  Chose one of these channels for each AP, a different channel for each, and try to avoid sharing channels with other wifi sources.

Thanks for your replies. So, the handheld will connect automatically between APsSSID without disconnecting if I use the same SSID? Or do I need to configurr something else?