The value depreciation of the hardware alone is going to be significant. Probably enough to pay for 3x ~$20 subscriptions to OpenAI, Anthropic and Gemini.

Also, if you use the same mac to work, you can't reserve all 128GB for LLMs.

Not to mention a mac will never run SOTA models like Opus 4.5 or Gemini 3.0 which subscriptions gives you.

So unless you're ready to sacrifice quality and speed for privacy, it looks like a suboptimal arrangement to me.