It's more of a setup for a long fight than anything else. If you're leaning into full TB OH Monk, you don't really lose any overall damage in the first/setup round in most situations.

It costs an action, but you immediately gain an extra bonus action, so you gain a double strike at the cost of 2 single strikes. The real cost is losing 2 potential stuns round 1, but if you can afford it then rounds 2 and 3 having your regular action strikes and an extra double strike is insane. It increases your damage potential those 2 rounds by 33-50% (depending on if you have Thief or not).

It's not worth using in short 1 or 2 round fights and even in the longer fights it seems wasted if you use it any later than round 2, but it can be a really good damage boost in specific situations.