Thanks @RenanAraujo! I do recommend asking Gavin and Misha to weigh in on the value of this, but I responded to Austin on what my best guess of the value is from the few talks we did.
1) We have not had that many guests - we finished setting up recently, and most people who signed up to come have signed up to come in 2024. I do think we may push ahead with something like "Prague Fall Season" but much much smaller in scale because of our smaller office and no funding, in order to get more people to come at the same time and enjoy the network benefits.
2) We hope to have ~5 people around all the time, and that seems basically sensible from the sign-ups so far, although probably starting from Spring.

@Austin Thanks! I think the main value for them was a country to work from in which they can both be visa free while they recuperate their visa days for EU/wait for US visa. They also gave a great AIS talk and spoke about prediction markets which is still highly regarded talk by EA Serbia members, so some cross-benefits there. I am unsure how much they used the office as I do not work from there, and we were not fully set-up in October when they were here.

I generally agree - I would not like to have an abundance of hubs, compared to the benefit of having few. I would not start a hub in Serbia has it not been some interest and the offer of this extremely cheap office space. I think CEEALAR and Fixed Point both do important and good work, but they are in the UK and EU respectively and that is prohibitive for some people (hell, I need at least ~3 months to get a UK visa unless I pay ~250 pounds to speed up the process!)

@RobertCousineau Hi Robert! In the post on LW you can see photos of the space. Cost is about 550 Eur per month with utilities (internet, electricity, water), although we would prefer having ~600 per month so that we can pay someone to clean the office weekly. The office has been used to comfortably work for ~6 people working at the same time without any problems, up to 14 could be done for meetings and such, perhaps not for quiet work. The quality of furniture and such is not up there with fancier workspaces, but is good considering it is the free furniture we inherited in the space - we would improve it if we overcome the funding limit, based on what people want to see here.
So far, we had a PIBBSS fellow come over, @gleech and @yagudin (hopefully tagged the right person :D ), all because they needed time to work near EU but be some time outside of it due to visa limitations for UK/Russian citizens. We have some people who want to come because medical care here is radically cheaper and they need it/don't have it in EU so they can keep working here while taking care of their health, and two MATS alumni want to work from Serbia in ~few months. We also have currently one and possibly more researchers from Russia who already live in Serbia who could use office space which they currently lack.
We have not done much active outreach until now as we were testing the space so this is the passive gathering of people, conceivably there would be more, and depending on geopolitics, there may be much more need in the future.