Bought a testo 550 a year ago. First six months set worked great. Then the problems started. Screen went blank one day.sent in to testo got repair. Two months later low side temp stopped working.sent in again. Borrowed brothers 550 while waiting for mine to come back. One week later brothers set somehow gets oil inside sreen and low side clamp reads on and off have to wiggle sensor to get reading.have to send to testo. Gauges ride in hard plastic case when not used and I unplug sensors after every use. Regretting my purchase. Can't go back to analogs. Will proprably try to sell them and hope ak900 doesn't dissapoint.