My 2 weeks with DeepSeek V4:
Pro is ~50% more expensive than Flash.
Both need babysitting.
Plan, split in small tasks, give it docs, types, tests, linter, best practice examples, etc.
Always start a new session when starting a task.
Do regular manual sanity checks, and tell it to find issues in the codebase.
I pay like $1,50 per day for Pro.