Was thinking about this at the moment. A local shop plus another that would give a discount on a bike I’m thinking about also offer 0%. Both will either do the discount or the 0%. One shop 10% off, the other 12%.
IF you have the cash and it would otherwise be sitting in a savings account, and IF it was in the best isa out there at the moment you would be marginally better off using the 0% but there is not a lot in it. If it’s sat anywhere else the discount is best financially. If the flexibility of having the cash sitting in your bank is useful to you, 0% makes sense if the money is somewhere sensible in the meantime as the margin is pretty minimal. Obviously if saving rates go up the gap widens making 0% even more attractive. Probably the best thing you could do financially would be to take the 0%, use the money you would have used to buy it to overpay on your mortgage (provided no penalty) and pay the 0% loan repayments off monthly with future savings.
edit – that was 0% over 3 years. If the 0% is over a shorter term (esp. 12months), but the discount remains constant, the discount wins every time.