Binomial is Better IF:
1. It is truly Bernoulli trials. That is, each "trial" (a piece of equipment operating for a month) has an equally likely probability of failure as any other piece of equipment, and there are no dependencies between failed equipment (if one item fails, it doesn't knock out four others).
2. There are no real world issues like burn in, burn out (ie Non-Exponential failure rates). No aging of equipment. Preventive Maintenance is OKAY, if it is CONSISTENT across all items.