My plane came with the 700 but now I'm replacing it with the 830. So if you're making the choice from scratch, I say go 830. Someone said the 830 is the same probes, but it's not quite true. It has more. It has RPM, MP, Oil Pressure, OAT, and perhaps a few others I'm forgetting. Also, I would put the unit in the unused slot above your CDI and left of GPS. You will probably spend more time looking/glancing at the engine monitor than most other instruments.
I didn't like the 700 because I was wasting too much time scrolling through different parameters. On the 830 they are all displayed simultaneously and in full. What kind of Mooney do you have? Is it fuel injected? Honestly though, if you're not going to be flying LOP or fine tweaking your leaning, this kind of precision isn't as important. I doubt you'd be saving much or anything by getting an expensive engine analyzer on a carbeurated engine.
PS I'd be ok with having my full name, N number, etc for Mooney pilot's eyes only. But I don't like the idea of someone googling my name or N number and finding all my posts that way. That is what is keeping me from posting that.