Overall Rating: 4.3 (of 5)
The Minor 2-5-1
Knowing which of these to use, and when, is the problem.
Obviously if you're in C major and the Bm7b5 appears as part of that key there's no problem - just use the C scale.
If you're in Am and the Bm7b5 appears (which it almost certainly will) then use the A harmonic minor.
However, if a m7b5 chord appears as part of a ii-V that doesn't resolve to the i chord then you can embellish it with the relevant melodic minor scale.
You'll rarely get a Bm7b5 as part of a progression in C but what you will often get is the Bm7b5 used in conjunction with an E7 (or E7b9) if the tune modulates into Am.
Here's an example of this using A harmonic minor (because this is a complete ii-V-i progression) then C major.