Does anyone have any experience with efficiency units?

[Neil Nagaria]

I'm looking at investing in 12 efficiency units. They range in size from 400-700 sq ft. ROI is 6% at current asking price. Not sure how much more rent I can get over the next 5,10,15 years. I have 8 single family homes and do well. I'm not sure if efficiency units would be parallel to the homes in terms of ROI. Appreciate any other input / information anyone else may have.