It's still extremely inefficient. 100kg worth of plutonium pellets in some RTGs will produce about 50 kilowatts of thermal power. 100kg of plutonium in an SMR on the other hand could easily provide 500 megawatts of thermal power.

The average US household has an average power draw of about 1.3 kilowatts, so assuming 100% conversion efficiency in the above cases, the RTGs could power about 38 houses while the SMR could power about 38,500 houses.

Given how expensive plutonium is, that thousand-fold difference makes RTGs a complete non-starter. And in practice an SMR would actually use uranium which is much cheaper, making things even worse.