I was wondering the same thing. Looking at some YouTube videos the AV500/600 seem to max out around 70-80 Mbps and the AV2000 seems to go up to around 200Mbps. This is on the same circuit and will depend on your wiring. Decent improvement IMO.
Does anyone with experience of these know whether I'd see much of a difference over the AV600's? I have 3 which perform really well but copying files to my NAS still seems quite slow :/ is it worth upgrading?
They are different - access point usually a single unit, mesh network is essential multiple access points in one combined network 'mesh'. If you need a powerline because of weak wifi signal, a mesh should be better than an access point alone.
Mesh better than using routers as access points?
Consider a wireless mesh network instead of power line, unless you live in a medieval castle with thick stone walls. Their performance is better and there is less degradation over time compared to power line adaptors.