Premix is 100% safe if you remember to do it.
Auto lube if it gets blocked by something/ one of the pipes perishes and leaks out or anything else goes wrong you have no lube in the affected cinders and that will cause damage.
The auto lube systems are generally safe but like anything mechanical/electrical when they fail you may not know it till its too late.
We are running the auto lube on my dads boat but the oil level gets checked after every use to make sure it is using oil.