^
Just plain Client Bridge provided by DD-wrt. (& wpa2 personal and yada daa).
The 1st bridge is an Atheros chip box on dd-wrt, the 2nd is a Broadcom box, but they work pretty good.
Lot of radio/WiFi signal activity here in the neighborhood.
Have not picked up on mesh yet, I should study a bit on that.
Summary:
One DHCP server is best, so you avoid double NAT issues, and your local network isn't segmented.
Mesh has hand-off, so a device that moves around (phone) could be on a call, change from one router to another - and it doesnt know. No dropouts, no packet loss etc.
They also route the traffic smarter, like a switched ethernet hub - so in a setup with say 5 mesh repeaters, traffic only takes one route - it's not duplicated along all of them
In your setup, traffic isnt duplicated - but it is segmented, so devices on network 1 cant see or talk to devices on network 2, but they both have internet access.
The second router is limited in without port forwards, inbound traffic cannot reach those devices - it hits router one who says "what? i dont need this" and ignores the traffic (P2P games and anything player hosted can utterly break, here)
Edit: If you can get "client bridged" working, DD-WRT solves half of this by keeping them on the same local network, but the wifi aspects are independent - no client handoffs, and they can't coordinate to reduce interference (so they'd need to be seperate channels) and if the hardware doesnt support multiple networks you're gunna have bandwidth issues (see repeater bridge below)
WDS seems to be their preferred method, but requires matching hardware on all devices
Linking Routers - DD-WRT Wiki
Client is meant to be used as wifi->many wired, and works great there (especially in bridged mode), but if you add it's own wifi network it's simply going to act like a seperate wifi network, and not part of a unified network like mesh
Repeater (of any kind) is always a bad choice because the wifi hardware of the second router is being used in both directions at once on the same channel - so at best you halve your speeds, but in a noisy environment it can be even worse