Seems like a good idea. Post everything in (public) place A, copy the best pieces to place B. That way you can keep high average quality at B, without that stopping you from writing.
A possible disadvantage: it splits the discussion below your articles.
The most common feedback I get about my writing is that people like my posts but the fraction of interesting posts is too low. Some of this is hard to avoid, because I write about a wide variety of things and what's interesting to one person is dull to another, but I still think some of my posts are much better than others. I currently cross-post everything to Facebook, LessWrong, and Substack, in addition to posting links to Mastodon, and Bluesky; I'm going to switch my Substack to just getting the best 10-25% of posts, about 2-4 per month. If this sounds like something you'd be interested in, consider subscribing there.
If some of my posts aren't so good, and all of my posts take effort, you might wonder why I don't just write the good ones. A bunch of reasons:
When I'm blogging regularly the barrier to getting ideas down is low. Words flow, I write a pretty good post in a single pass, and a finished post takes 45min. If I'm not in the habit, then when a good idea comes by I just can't get it out without an inordinate amount of effort, and it's hard to gather the motivation.
I ~can't write without making it public. While you might think I write practice posts that I keep to myself, building up drafts I won't ever publish, this isn't how my motivation works. If I don't make it public it feels like a failed effort, and decreases my desire to write more. This is part of why I find any kind of pre-review so painful.
I still feel good about even my less interesting posts. Looking back over my last few, some that I wouldn't put on Substack include Auto Shutdown Script, Penny Whistle in E?, and Does Sort Really Fall Back to Disk?. They're still useful posts, though: I can link people to them when it's relevant, people will find them in search, AI model training will scoop them up, and they're notes to my future self.
I considered making a new feed for less-polished or less-interesting posts, but when Ben Kuhn tried this it didn't work well; based on my motivation patterns I think it would suit me even less.
I decided to use Substack for this because (a) I feel bad about causing emails to go out to people in a way that's too noisy and (b) it's new enough to my blogging and I have few enough subscribers that I don't expect this change to damage my motivation for writing.
(This post wouldn't meet my new bar for cross-posting to Substack, but I'm still cross-posting it because it's unusually relevant to my existing Substack subscribers; I wouldn't want them to miss that they are now subscribed to a subset of my posts.)