pro and cons are here
Advantages of Using DD-WRT firmware

The router gets increased stability
Less lockups/crashes
Less connection drops (I'm looking at you, generic VPN protocol!)
Support for a larger amount of concurrent connections
The ability to increase your wifi signal strength (stock firmware has really weak wifi transmit power)


Disadvantages of Using DD-WRT firmware

Unifi home users (VIP5/10/20) lose IPTV access
You lose TM support for your Unifi service (it was pretty much non-existent in the first place!)
You probably void the warranty on the router
You might brick the router if you don't know what you're doing

more explanation see here
http://unifi.athena.my/ddwrt_guide.php

if make two router, then why not get new one to replace DIR615 then will be ok

no u cant.

why change to dd-wrt ? is it because of the locked function?
if change to new router then problem will be solved

but i heard that DIR615 wifi signal quite strong

vip20 install complete~~register at 11th feb~~install today~~very fast~~

Maybe u use a fakap firmware version :-)

3:30am. I think IT guy forgot to configure timezone to GMT+8. :-)