I would echo what many other people are saying - decide what your reasons are for purchasing, is it purely based on returns or is it somewhere you'd like to also vacation?

You'll also need storage space for cleaning supplies, change of linens and towels and small miscellaneous items like a first aid kit, extra batteries, flashlights, broom, vacuum, etc.

The more common one I'm seeing is just pure speculation that the value will continue skyward in the future.

Was having a fun, purely academic conversation with someone and somehow the topic went from the stock market, ETF's, to real estate, to BRRR's and either he or I or both us came up with this and wondered is this a legit strategy that others have used?

That looks like your problem - only 3% down (can you get that conventionally if its a pure rental property - i'm not 100% but I don't think so) - with that leverage (97% LTV), pretty much nothing is going to pencil.

In other words, how would I calculate the return (from a purely financial standpoint) of "investing" in a primary residence vs renting and putting the money elsewhere (perhaps even into an investment property, but also considering buying a business)? 

They're designed for owner occupants but could be something in which you occupied for a duration of time and then converted to a pure investment later. 

This is typically more favorable than financing for purely investment properties.Income Generation: You can rent out the other half of the duplex.

Battery tech is changing the game but it's insanely expensive. 

Batteries are at 98% so that isn't the issue.For those that have other smart locks, have you seen anything like that?