Wireless Ethernet Bridge mode vs. just having a second access point

What's the difference between having a second router configured as an access point vs. putting Tomato or other firmware on it and enabling Wireless Ethernet Bridge mode? 

I have a rather old router I put upstairs as a second access point. I have it with the same SSID and WPA2 just on a different channel than the main router that runs Tomato. It seems to work, but the device itself sometimes craps out so I am considering what to do with its replacement. I could go cheap or I could make sure it's Tomato compatible to take advantage of Wireless Ethernet Bridge mode.