Seeking Alpha is a source of ideas and opinions. PnL App is a record of what you actually did with them.
Seeking Alpha aggregates investment analysis and opinion from a large community of contributors, useful for idea generation and different perspectives on a name. PnL App has nothing to do with idea generation, it tracks the trader's own behavior once an idea, from Seeking Alpha or anywhere else, becomes an actual position.
PnL App tracks the behavior behind every trade, no matter where the original idea came from.