pros and cons of a flat tappet cam

Pros,
Hydraulic flat tappet cams are cheap.
They're reliable... Come on, they came in almost everything for what, like 50years?
Up to a fairly high performance level, no issue.

Cons,
Break-in.
Only good to a certain performance level.

Mechanical, good to higher performance levels.

As for oil arguments, once past break-in any good oil should suffice, and if you must, go for a zinc additive.

Obviously, rollers are the hot **** in this day and age, but flat tappets can still do it....