Is the Budget Reallocation tool free?
Every account gets one free run, then it's 1 credit each (free monthly credits cover normal use).
Will it tell me exactly how much to move?
No — and it won't fake that precision. It ranks your channels by real ROAS/CPA and reasons about where budget should flow and what to test, but it's explicit that diminishing returns and attribution mean you should shift budget in small, measured steps rather than make dramatic swings on these numbers alone.
Why does it keep mentioning attribution?
Because the ROAS you paste is almost certainly last-click or platform-reported, which over-credits some channels (like branded search or retargeting) and under-credits upper-funnel ones. Being honest about that is the difference between a useful tool and a misleading one.
What do I need for each channel?
Spend, plus either revenue directly or conversions and their average value (it'll multiply those for you). You need at least two channels with performance data to compare.