I'm not a gram counter by any means so the added weight means nothing to me, the pack size is what I care about and this bag meets the requirement.
I still don't see any valid reason to not use it as a TQ when I want too. The zipper, as mentioned, can be a bit bothersome but it's not a nail in the coffin by any means.
Also, how much did your cottage 750 FP UQ cost? I would have to estimate for versatility and price point the Kelty SB was a better deal for me.