I believe IB is extremely safe.
I would also emphasize that You can't compare the safety of brokers, simply by comparing their insurance coverages. You must also consider the quality of their risk control. I am not aware of any broker having risk management as rigorous as IB's. The likelihood that insurance coverage will ever be invoked, at IB, is therefore far less than it is for brokers with weaker risk management.
The safety of IB is underrated and underappreciated. People tend to seek the lowest commissions, without considering safety. I think it's very healthy now that people are starting to think about the risk of loss due to broker bankruptcy. But I think IB is rock solid safe.