OK, here is an example that came up three or four times in the Out of the Abyss game I play in.
I had a tempest cleric with shield master feat. Also in the game was a warlock with repelling blast. Quite often, foes would get next to the warlock and disturb her eldritch blast casting. Our tactic was for my character to push them 5 feet back and then retreat 5 or 10 feet. The warlock would then cast eldritch blast (no longer at disadvantage) and push the target back 10 feet. She would then retreat her full move behind the cleric. Now, the foe is out of melee range of the warlock. The feat meant I had two chances to push the foe (action and bonus action if the action was resisted).
In that game, the second bullet of shield master came up a total of zero times (how many single-target DEX save spells are there, anyway?). The third bullet point only came up once or twice.
I don't think I ever knocked a foe prone. That would have disadvantaged the two ranged damage dealers (the warlock and an archer).
Overall, my feeling about the feat is "OK". It was nice but very situational.
Additionally, there were other things that competed with the bonus action (healing word, spiritual weapon).