Installed it to check what all the drama was about, checked only on tumblr.
Reviews claim news articles and such are often marked correctly, which I have not tested and can thus not comment on.

Accounts marked green were a crapshoot between "good trans advocate" and "at bare minimum raising eyebrows with their stances on transmen or enbies".

Meanwhile of all the accounts I follow that were marked red, multiple were positivity accounts for more 'niche' or 'controverse' topics - including accounts for enby-related stuff, xenogenders, or even one that just spreads positivity about all types of plural systems.
At least one of which had nothing to do with transness at all? But I digress.

Multiple accounts that were outspoken about transmasc issues who dared occasionally point out transfems who were hostile towards transmascs were also marked red, despite not being transmisogynistic.

As such, my final verdict:
Either due to a lack of moderation, deliberate misuse by the community, or both, this tool has gone from a good idea to falsely marking innocent users as red for mild disagreements, oft with transphobic intent (how ironic).

I cannot reccommend using it.
If you still decide to use it, at least don't take the red or green markers as definitive - actually check accounts, and consider critically why someone might have been marked green or red.

(Additionally, accounts that praise shinigami eyes to the high heavens whilst unwilling to admit any flaws with it are sus as hell, which is useful when using tumblr as well.)