Do ADU’s hold there value?

[Cesar Perini]

I live in So Cal and I'm looking to invest in rental property here. Prices are so high that rental income never exceeds the mortgage plus expenses. But, with the new ADU laws passed in 2020, ADUs are a good way to get great CF. The CF from an ADU can easily cover construction cost and cover the negative from the existing house. I'm just worried about the value add on the property when building an ADU.

My question is probably for appraisers out there. Does an ADU hold a good value? Since there aren't many comps yet it is hard to get an ARV. Can you use a duplex as a comp as long as it's the same SF and room count as the ADU?