It’s not a new debate. Replaceable vs fixed. Making steel frames, we opted for fixed. In 7 years and over a thousand frames, we haven’t had a broken hanger yet. A replaceable hanger might save a derailleur. It might not. Often you end with both a broken derailleur and hanger …and hangers that can actually save a derailleur can be flexible enough to compromise shifting. Then there are complications that come with detachable parts and the additional hardware they require. Less hardware if possible, is a good thing. The seat post size on this frame is 27.2, not 30.0.