Yeah, early on it worked okay. Not as good as when I used RealmWorks or MapTool for in-person games with a horizontal monitor acting as a battlemap with minis on it.
Then the community developer stopped supporting it and it broke. The League of Extrodinary Developers took it on and it would work and then not. It seems to have finally stabilized, but by that time I had already moved to prepping all of my maps for dynamic lighting.
In my current campaign, I'm using pre-prepped maps so I haven't had to rely on it. But I've tested and played around with it fairly recently and I still don't find it a smooth experience. It isn't integrated and I'm still not exactly sure how it interacts with the core scene settings and core lighting controls. If I use it more maybe I'd get more comfortable with it.
For comparison, the D&D Beyond Maps manual fog of war works very well.
The problem is that the Foundry community has very little interest in manual fog of war. Foundry really shines with all of the advanced lighting and line of sight features. Manual Fog of War has gotten onto development priority polls over the past few years, but receives very few votes. I had subscribed to the Foundry patreon to get voting rights, but eventually cancelled. My priorities just don't match those of the majority of Foundry's users (or at least those invested enough to pay for the rights to vote for new features).
Normally, I don't mind dealing with the issues that community modules bring (development stopping, breaking when a new version of Foundry is released, etc.) because most provide DM quality of life or eye candy features. But fog of war is a core, fundamental feature if you want to run a low-prep, sandbox game. Other VTTs do it better and I have yet to find anything that does it better than Map Tools (though the networking hassles of configuring it to host games online prevent me from recommending it for most people looking to host online games).
If I were to run a low-prep, open sandbox campaign, I wouldn't use Foundry. If I were to run D&D again, I would likely just use D&D Beyond. As much as I like Foundry (and it has been almost a separate hobby in itself for me over the past 4+ years), I think a lot of fans oversell it those looking for a VTT. I would never recommend it for someone that wants simple, low-prep battlemap functionality.