The best candidates for a lifetime deal are tools you use every week, where your needs are stable and the category is mature: scheduling, e-signatures, forms, email newsletters and social scheduling.
Be more careful with tools where your usage will grow fast or unpredictably — for example, high-volume automation or AI credits. In those cases pick a higher tier than you need today, or confirm that extra codes can be stacked later.
A simple rule: if a subscription costs you more than the lifetime price within 6–12 months, and the vendor is actively shipping, switching is almost always worth it.
Finally, keep one paid subscription for anything mission-critical where you need enterprise support or compliance guarantees. Lifetime deals are perfect for the long tail of your stack.