It all depends on the type of flying you will do (day vs night, VFR vs IFR), the characteristics of your aircraft, the weather you will fly in, your skill level and your tolerance for risk.
It is not possible to ensure that a D100 failure will not occur. You have to assume that it could fail, and then consider the effect. Could you safely get the aircraft back on the ground with an acceptable pilot workload? If so, there is no need for backups. If not, then backups should be installed. Only you have the info to make this decision.
