I have the BHC speedball and run really good NOS tubes (GEC 6080, Tung Sol 5998, RCA clear top 12au7, etc.) and it's a good setup.
The LTA MZ3 to me, is a completely different level. It should be at 10x the cost, but putting cost aside, the main differences noted on the MZ3:
Bass has superb extension and is very tight. There is a visceral presence/resonance to the low end that I can feel and it's so precise, where on the BHC is not well-defined. Midrange is also very detailed and vocals shine through quite nicely. It's no mid-forward, but really balanced. The upper midrange and high frequencies are really what sold me. The detail, separation, and crispness of the high end is amazing. I can hear strings bright and clear, percussion like cymbals, chimes, etc. sound very defined. I can hear the snap of the nylon tip of a drum stick on the mylar drum heads. The detail is super realistic, but not fatiguing or analytical. The upper midrange and highs on the BHC do not have anywhere near this level of clarity, definition, or crispness.