It's designed as a mesh kit and it can do the same (and much more) with OpenWrt on them. I use them in different locations as either a mesh system or as main router + dumb APs to increase coverage.
You could also sell the one(s) you don't need or you just keep them until you get another idea what to do with them 
While I use them for VPN, performance is limited by the 40Mbps ISP connection. The mt7621 is not the fastest CPU, I've read reports [1-3] that it can achieve about 150-200Mbps with Wireguard and less than 50Mbps with OpenVPN.
So it depends heavily on the VPN solution used and on your requirements - what is "high throughput"?
[1] Best VPN Performance Router under $100? - #41 by eginnc
[2] Netgear WAX202 WiFi 6 $30 at Amazon - #162 by eginnc
[3] https://www.computerbase.de/forum/threads/wireguard-testversion-von-fritz-os-7-39-fuer-die-fritz-box-7590-ax.2057956/page-10 (German)