After working with so many relay modules, be it an 8 channel module or a 4 channel one. Or a single channel one. The problem with EMRs is that they are really big for home automation products. I have made commercial solutions incorporating arduino nano which are really cost effective. But the problem is how do i bring the size of the whole module down where relays take up a lot of space.
Alternative that I would like to suggest:
1) SSRs ( really expensive)
2) BTA16 with MOC 3021.