Thank you for your post! I can appreciate how important it is to ensure you are getting the speeds you are paying for according to your Internet plan.
It can be difficult to guarantee a particular speed via Wi-Fi due to numerous factors that can degrade the signal such as attenuation and interference. Speaking from experience as I also have the 500U plan but no mesh network setup (my home is smaller than average so a mesh network is not required for my setup) I consistently get around 250 Mbps download and 25 Mbps upload on the 5G network on my Samsung S7 Edge. I have gotten as high as 330 Mbps download but never any higher than that.
What speeds are you seeing via Wi-Fi with your Eero Mesh Wi-Fi System?
Well it looks like the Eero is AC capable (though, doesnt really say WHICH). Tri band.
Overall, it should technically be able to do up to the plans speed. That would be under the BEST circumstances.
Getting proper wifi coverage, and at the top speeds.. is always a chore even with the best equipment. The Mesh should be able to get your coverage if set up alright.. But any sort of mesh or repeaters, will only repeat what the best signal is. So you want to place your next mesh node somewhere its getting a GREAT signal.
Beyond that.. there are a lot of other factors. What the end device has.. Any form of interference (cordless phones, microwaves, and even just metal studs in the walls)