Today, he cleared all of the bats, completely rebuilt the chase, re-flashed, sealed, and got everything battened down in time for the guests tomorrow!  

I find with time, they always leak, as the joints just don't stay sealed as well.

You really want a rookie putting a waterproof seal on the top of a building?

After they were purchased, they were filled out, sealed into envelopes and mailed to me via certified mail.

Its not without hassle though, that's an important distinction, tuckpointing, brick sealing, and potential wall separation/collapse are always considerations. 

I have a good roommate that pays on time and just does his own thing.. however a few weeks after he moved in (mid-Feb) I heard his toilet (main toilet) running and found he had hooked it a few links higher so the flap wouldn't seal.

To make a long, expensive story short, we discovered that builder failed to insulate an entire 3rd attic space and didn't seal wall cavities up in the main attic or insulate chases properly (Inspector failed too). 

Once you start using it, keep a piece of plastic on top of the remainder inside the can, and also seal the can tightly with the lid.

This makes LVP and good choice for the LTR investor.Porcelain is highly durable, easy to clean ( if sealed properly) more expensive, and harder to install.

If you can submit plans, likely sealed by an architect or engineer, and get the official approval before buying, that would be safest.