Ok for anyone wondering there are quite a few difference between the new AX4200 and the MX5300. They have just dropped the price of the solo MX5300 from £350 to match the AX4200 at £250 also.
AX4200 MU-MIMO Tri-Band Gigabit, 600+1200+2400 Mbps
AX5300 MU-MIMO Tri-Band Gigabit, 1147+2402+1733 Mbps
1.4GHz Quad Core Processor
2.2 GHz Quad-Core Processor
3 Gigabit LAN + 1 Gigabit WAN
4 Gigabit LAN + 1 Gigabit WAN
40+ Devices
50+ Devices
2700 square ft coverage
3000 square ft coverage
Flash: 512MB; RAM: 512MB
Flash: 512MB; RAM: 1GB
2.08 lbs
3.5 lbs
Both are same size
Both have USB 3 for external storage.
So I appreciate the AX4200 is the new 'Flagship' as it's way cheaper. But also isn't quite as specced out as the older one.
I just bought an MX5300 at the weekend for £350 and now its dropped to £250. Just spoke with amazon chat and they're refunding the difference.