Has been released.
I think I can recommend that Beta version, I have been using 2.53 for a long time without bigger problems. But you should keep in mind that there will be no way back for your existing User Profile after you will have used it with 2.53.
You should do a backup of your User Profile before you launch the new build firrst time.
Download and more information: SeaMonkey 2.53.3 Beta 1