> I'd skip M5 and M6 chips for LLM work and wait for a year for M7.

Another note on this, it's likely the M7 ultra will be released around 6 months after the M7 Max, if the M1 and M5 are taken as reference. So the M7 ultra may be delayed until early 2028.

I'd be worried about securely erasing my data when returning a leased model.

What do you do with older hardware that you've bought? Do you not wipe it and resell / donate?

If you encrypt from day one then a lease isn't much different.

Just delete the encryption key.