Recently? I completely agree their systems, initially, were not too smooth. But from what I have seen lately it's much better.
Sometime ago, maybe 2 years or so, I looked at doing something similar. After some research I tried
Spotipo. Trying something similar to what you are doing. Back then it was pretty rough but seems to have matured. But was not able to get any of my customers to bite. I've not looked at it recently but they are still around and seemed to have matured.
I do know from work I have done for other companies that many use Meraki and Ruckus. But they require their controller as well and those packages are pretty expensive compared to Unifi, including Ubiquiti's controller.
What I was looking for was to include joining with social media accounts in addition to the regular guest login.
By advertisements were you looking at something like what
Boingo does at airports and other places? A popup advertisement for a relevant business, then join?
As far as mesh is concerned that's part of the hardware system itself. Independent of any wifi gateway service.