Well to begin with, you're lucky you came here and asked first. That 3T fork has a tapered steerer (the "1 1/2 " part that you missed in the listing description/ title). I'm pretty darn sure your frame does not have a tapered headtube to properly match and interface that fork.
It's so cheap because near nobody buys aftermarket tapered steerer forks as usually the ultra high end carbon road bikes that come with a compatible headtube has a better fork to begin with. And in circumstances where they would have to replace their fork there's warranty and if a crash is serious enough to damage such a fork, the frame is usually done too.
Wheelandsproket is a reputable seller anyhow.

I would avoid that aventon fork, it's just a cheapie road fork that they're selling for premium to make profit off unsuspecting fixie owners. Carbon steerers are not really something to care about; they're overhyped unless you have a bike that costs a couple months worth of paychecks.
If I were you I would save up a couple more bucks here and there and invest in a better fork with fixed gear oriented rake. Leader has some good thoughtful offerings unlike aventon.