The BM is a far better pedal if you are after just boosting the amp. Basically using it as a clean boost (dime the level and zero out the gain for example). The bad monkey has a bit more level on tap then the TS9 as well so it can push those preamps a bit harder which is a plus for most applicaitons. Also the TS9 colors your tone quite a bit vs the bad monkey and what little coloration the BM has it can be taken out with a simple mod. What all this adds up to is the BM will tighten and add a bit more gain then your standard OD pedal like say a TS9. So that said its alot better clean boost in my opinion. More boost and more transparent..
Now the BM vs the TS9 as a stand alone pedal. The TS9 beats it hands down if your using it to mimic an overdriven tube amp example actually turning up the gain knob then the TS9 is your pedal its going to sound better and warmer. So using the pedal as an OD, the TS9 is a better pedal in my opinion. And the end result for metal I love the BM and it does a great job of pushing those preamp tubes harder allowing the amp to get into the metal realm without needing a ton of gain from the amp. And it really tightens up the amp in the process.
And reliability isnt an issue both are great solid pedals...
The TS9 is good and so is the BM but you might want to look into the Maxon OD-808, i found that it really is the best peddle for boosting your tubes. Unfortunately Maxon have recently discontinued this peddle, but you can still find it around.
