Smartphone or DSLR?
IMHO most cameras these days with stabilization do pretty well w/o flash. Unless you are bouncing flash or have a diffuser I find no-flash much more pleasing.
As to how distracting, if you only take one picture and know enough not to have to CHIMP, why not, no more distracting than all the other things that happen in restaurant. with lots of talking etc. etc. IMHO.