They can be — if the tool is already useful today, the company has a track record, and there's a refund window long enough to test it. The payback bars show how quickly a deal beats paying monthly.
What's the difference between AppSumo, RocketHub and a direct deal?
AppSumo and RocketHub are marketplaces that sell lifetime deals on behalf of software companies, with their own refund policies. Direct deals are codes or offers from the software company itself.
Do promo codes work on renewals?
Usually not — most codes apply to your first billing period only. Each deal says what it covers.