Why not? Setback posts are common to dial in a cockpit, and AFAIK the stock inbred post is a setback (I'm too lazy to go check mine) so I imagine a lot of people are using that one. I just went to a non-setback and moved my seat back on the rails.
I’m tempted to use a setback seatpost on my Inbred 29er… but after having raced it in a CX race a couple weekends ago with a standard seatpost, I am going to hold off. I’ll be racing it again in a few days (Saturday the 7th) and will re-evaluate then.
If I were riding more technical terrain I’d probably put it on there though. For getting the “attack position” just right it seems easier to manage the front/back balance with the straight seat tube. Your mileage may vary.
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