I guess from a physics standpoint, one would expect an SMR to be somewhat less fuel efficient in that a nuclear reactor is essentially a furnace and the surface area to volume ratio favours a larger design to retain the heat. SMR proponents like to spin this as a "feature", however, in that they would be less likely to meltdown and that safety trumps efficiency in reactor design. Another point they claim from the safety standpoint is that if you had say a dozen SMRs replacing a single traditional reactor, you could routinely take one off-line for inspection/maintenance without a huge hit on power generation.

I don't know enough about this and most of what I read is anecdotal though, so take it with a grain of salt. There may still be a case for them in northern communities, many of which are off the grid and use large diesel/gas generators? I guess it would depend on how well SMRs can follow load, which has tended to be a problem with nuclear power.