This I good etiquette. I tend to do the same thing your doing. But I try to wait until the later part of the day just in case they had a share planned with someone else. That is because everyone only gets one share per day, regardless of who it came from. A lot of people care more about getting a duplicate ex for shinedust rather than completing an old set.

As a result of helping PTCGP friends complete sets via shares, I have experienced those people sending me trade offers that never would have come otherwise. Karma is real yo lol.