How they really differ
OutlierKit works before you film: it helps you choose topics with proven demand. TubeBuddy works mostly after you film: it helps each upload get found and lets you test and manage videos at scale.
New channels usually gain more from picking better topics than from fine-tuning tags, so research tends to pay off first. As your library grows, workflow tools like bulk edits and A/B tests become more useful.
Both are subscriptions with free or trial options at times. Check current plans, since features move between tiers.
Using both
Pick next month's topics with OutlierKit, then use TubeBuddy when you upload to tune titles, tags and thumbnails and to test what works.
The verdict
OutlierKit to decide what to make, TubeBuddy to optimize and manage what you publish. Small channels should usually start with research.
Want the full write-up on each? Read our OutlierKit review and TubeBuddy review.