I don't think they're for China at all.Doesn't make sense as trip wire force, small unit like that is not enough to justify conflict with China. Beside, if US want to go to war with China for Taiwan they don't need that kind of excuse to begin with.
Also, in an event of open war, that base would be first to capture or destroy anyway. The black ops on mainland also too much risk for geopolitical image, if any of them got caught.
The move seem like US still want to flex themselves on Taiwan with minimal risk while also use this unit for training and observation post.
Kinmen has been a hotbed for Taiwanese defection. In 2023 a Taiwanese officer swam to Xiamen from Kinmen. Lin Yifu, a current member of the State Council, also swam from Kinmen to Xiamen.
These look like barrier troops to me, to prevent defection in peacetime and surrender in wartime. That is also why they're described as "trainers". Their role is in controlling Taiwanese troops.
