Curious what are the main benefits ? (I've only ever used DD-WRT and OpenWrt)

I use Tomato too, but I wouldn't say it offers many benefits over OpenWrt. The main thing is that routers based on Broadcom chipsets often only work with very old Linux kernels (such as 2.6.xx kernels), as the drivers are closed source. For these routers, the primary third-party router OS choice is to use Tomato.