I now used Firsty "Free" in multiple countries, and I've got to say it pretty much works as advertised. Details in the post linked to above, but basically after watching an ad (10-30 seconds), you get 30 or 60 minutes of free "slow" internet. Slow in that it's fine for email/messaging/Maps/Uber/etc. Web browsing is possible, but not fun. Video/etc just isn't an option.

In other countries I've used this as access to get another eSim install, or whilst in transit, etc, and it's worked fine. But I've spent the past week in Dubai and decided to try using Firsty Free as my only provider. For this trip, I knew the vast majority of the time I'd be places with Wifi access, but I still needed something to bridge the gap when moving between those locations. So every time I was walking through the lobby of my hotel, or out of the office, etc, I'd fire up the FIrsty app, watch an ad, and then get enough internet to get me to the next location where I'd have wifi.

All up, it worked fine. I don't know that I'd do it again, and I certainly wouldn't for a location where I didn't know I'd be simply moving between a small number of locations all of which had wifi, but for this trip it was fine. On the last day I did activate the free 24-hour SIM card they give out when going through immigration as I knew I wasn't going to be near wifi much of that day - without the free SIM my plan was to instead try out Firsty's paid access, but in the end I didn't need to do that.