Verdict
The A1 wins year 1 by sticker price ($400 less). The MK4S wins year 2 onwards by failure rate (2.1% vs 4.5% measured), which translates to ~$240/year less wasted material on a 1,000-print/year shop. Break-even on the price difference: about 2.5 years at 1-2 hour avg prints, ~4 months at 4+ hour prints because failure penalty scales with print duration.
Buy the A1 if: short prints (under 60 min), beginner or intermediate operator, budget under $500, multi-color matters (AMS Lite is cleaner than MMU3).
Buy the MK4S if: long prints (4+ hours), engineering materials (PETG-CF, ASA), planning to keep the printer 4+ years, prefer open-source serviceability over ecosystem polish.
Read the full deep-dive: Bambu A1 vs Prusa MK4S cost analysis.