Check Prosport prices with Nick at Gaugeplace. You'll get better customer service from him than Xyberauto anway.
Plenty of stories of gauges of all makes reading slightly inaccurate (0.1 bar out on boost etc) but as Gerry says it needs to be consistent. I'm going to check my own oil temp sensor accuracy before next trackday, as it claims a max of 103C on track with no oil cooler, whilst running 1.6bar, sensor above #3 cylinder. Bit sceptical of its accuracy, but it 's very consistent.