Kinda, Overpower is nice in some situations, but it has a few really annoying drawbacks - it's a frontal cone aoe, and its very subject to lag and monster movement. It's also expensive TP wise, which means that missing a few on a group of mobs is really punishing, and probably means you have one or more mobs now chewing on the healer.
The worst part by far though is that unlike Flash, it breaks sleep. This means that Flash is probably going to be stuck permanently in my cross class skills instead of another damage mitigation cooldown.
Granted, that's mostly for dungeons, for tougher boss fights I don't need Flash so I can swap it for a different cooldown (... and then you usually don't need Overpower either

)
If you're in an aoe heavy group that isn't using sleep, then Overpower does shine more - or if you can coordinate with your blms to not sleep until you lock aggro with 2-3 overpower hits on the whole pack - but that's so annoying to do in pugs I just use Flash instead instead of explaining it every run.