Bruno Tilz 231-B 2 vs Bruno Tilz 310-M 12
The Bruno Tilz 310-M 12 has a wider cup diameter, the Bruno Tilz 310-M 12 has a larger throat opening.
Cup Diameter
The Bruno Tilz 310-M 12 has a cup diameter of 32.50 mm / 1.2795 in compared to 32.00 mm / 1.2598 in on the Bruno Tilz 231-B 2 — a difference of 0.50 mm / 0.0197 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a shallow cup depth, so the sound character from depth alone will be very similar.
Throat Diameter
The Bruno Tilz 310-M 12 has a wider throat (7.40 mm / 0.2913 in vs 7.20 mm / 0.2835 in). A wider throat allows more air through, increasing volume and projection but reducing resistance.
Which is better?
Both mouthpieces are categorized as "Catalog" — the physical dimensions above will determine which suits your embouchure and playing style better.