aside from being able to control 4 more devices... you can now have temp monitor in your DT and sump & the ph probe for your cal reactor or have it monitor your tanks ph... definitely worth it... I got mine on sale a few weeks ago for $229 shipped..I thought that was a steal
+1, buy what you need. You can still find it for $100 at a bunch of places even though msrp is $120. Try to make sure to get a new RKL that comes with the splitter and V2 of the system interface device. Otherwise you'll need to ship the SID to DA to get it updated to update the firmware.