Unfortunately express have 100mbps ports.. not industry standard gigabit. So they are relic from bygone age.. good enough for airplay but nothing else.. and really work much better wired than wireless.. so they should be OK but due to the much slower ethernet will really slow down your network.
It is really hard to find products with the form factor I would like. That is a proper AP with 4 or 5 gigabit ports.
Most mesh units are designed to sit on a table or the like.. whereas AP are designed more for ceiling or wall mounting and usually have only one or at most two ethernet ports.
My standby is routers that come with AP mode.. preferably ones like Asus which do actually have a built in mesh as well but they are expensive. You are also after the best possible wifi signal and may as well buy AX products now.
I do like the TP-Link EAP range.. but they are ceiling mount design. You need a controller.. either a small unit or software on PC or Linux.. no Mac software sadly.
Another possible unit which is gaining popularity is Xiaomi A lot series.. The AX1800 is very cheap and has mesh extensions.. which you can setup fairly easily but should also work in AP mode.. it has 4 gigabit ports and should be reasonable. Lots of youtube videos with people using them so have a look. At the moment that is what I would jump to.. having tried Unifi, EAP, and lots of cheap routers which I get second hand off eBay and work perfectly well for my usage.
You can plug the express into the AP by ethernet and use them with wifi turned off. The result will be 200% improved wifi at least. And as AX products become the norm.. more and more will improve the speed and efficiency.
You can also stick to your main router as long as it is fast enough for your internet and MUST have gigabit ports.
The Xiaomi English firmware products don't see a lot of updates so using for AP/Mesh duties is fine and not going to make you subservient to Chinese firmware.