If TBN was actually dps neutral, then you could certainly throw it out on random autos. It's not.

The dps value of TBN is variable. In some cases the blood gain is greater than the MP cost, as tends to be the case during raid burst windows. On average, though, it works out to be a minor dps loss.

This shouldn't discourage you from using it when you need to mitigate a cleave or tankbuster. But it's a bit of a waste to use it frivolously. If you're unsure of this, look up DRKs who are trying to optimise for speedruns. You'll find a much lower rate of TBN usage in general (on the order of 1-2 times per fight). I'm not saying that you should necessarily emulate this, but it's worth noting.

I think that TBN's design tries to be clever with its resource juggling, but falls a little short because the rest of DRK's kit doesn't really take full advantage of blood - MP conversions. If it's supposed to be a focal mechanic, they should've gone the route of turning DRK into a full Zarya tank. Throw out shields, hit harder, throw out more shields.

From the way people talk about IB, you'd think that nobody ever uses it. If so, they should consider just replacing IB with FC in Defiance during the next job action crunch.