BTW, I've only occasionally worked with other mesh products. I had the very first Google Wifi mesh system, and it worked but I started experiencing some speed issues. I set up one of their more recent products and the process was weirdly difficult, with frequent failures on the side of their app and cloud services.

A "low end Unifi" solution is still pretty pricey, but looking at the Synology prices, I think it's pretty comparable. First, it looks like you need a full router for each of the access points. Do you know the MSRP? It seems to be out of stock most places but I'm seeing ~$250. So if you have three access points, that's going to be $750. These days, for home users, I generally recommend the Unifi Dream Machine, which is ~$300. Then you can add on any other Unifi devices in any configuration (they have a product for pretty much every use case). The access points are around $135-150. So basically you're around the same cost, perhaps saving a couple hundred.

The reason I suggest the Dream Machine is that it's more powerful than their basic gateway/cloud key pairing, and can do full DPI on a gigabit connection.

I think you'll be fine with whatever you pick. I think Unifi is objectively more customizable, and the rest of it is mostly subjective differences.