Pros:
- Goals
- Code of Conduct
- Up and Running
- PHP - I’ll explain
Cons:
- Front end needs a lot of work
- Methodical Development
- PHP
First PHP:
I am a PHP programmer (as well as Python and some other things). PHP can scale quite well. I know not everyone will agree with that - hey, we can’t even all agree on spaces (right) vs. tabs (wrong) 
So for me, PHP is a definite plus, as I would be able to participate far more in the server-side development than C#.
That being said, we seem to have already attracted a decent core of developers sufficiently familiar with C#/ASP.NET that I am reluctant to switch again, unless we have a really good core code in place to build upon.
Code Structure/Quality
I have not looked at the TopAnswers code (I know it is open source, but I don’t know if/how it can be accessed right now - I haven’t looked). But I suspect based on the relatively limited current capabilities of TopAnswers, and especially the relatively basic front end, that the code has a long way to go before it approaches the level of overall complexity that we currently envision for Codidact MVP (voting algorithms, moderator tools, etc.).
I also get the sense, which could be totally wrong, that they have not put the same level of methodical development (e.g., coding guidelines) that we have. That being said, the typical small projects that I work on don’t have those guidelines either - but those projects are typically between 1 (just me) and 4 developers, while Codidact already has a good size team and will likely grow quite a bit over the next few months. The Team & Tech Leads have both put a lot of work into building a group that will treat this as a truly professional project in every respect except money.
That being said, our goals align. We all want the same thing. We all want to have software that supports communities. Etc. So it does make sense to work together as much as we reasonably can.
PostgreSQL
As far as PostgreSQL, it is a definite plus that we agree on that piece of the puzzle. However, I suspect our schema will differ (there are a lot of ways to build a database), so if we either start with TopAnswers and move to Codidact when ready or if we don’t start with TopAnswers but want to bring in their existing community’s data when Codidact is ready, we will need to do some data conversion to make it all work. But working as friends that will be a lot easier than pulling data from SE as competitors.