If you take a look at what that tool is doing, it's all very hand waivey prompting that will sometimes work, but mostly not. You need to put agents on rails and the docs it produces are more like friendly suggestions.

Spoken like someone who hasn't tried one or perhaps both of those projects

Kiro is collaborative, but SpecKit is a bunch of templates and then wishes you good luck in your journey. It honestly reminds me of those unified process templates, which I guess all of those are great if one needs some structure to organize ones thoughts

As an alternative, SpecKit is also 0.x release so maybe in 9 months it'll be useful - or overcome by whatever 'ooh, shiny!' follows it