Router + NAS is probably the worst idea to have in the networking world.
Hackers can penetrate the routing layer then go into your storage and get all data.
Hackers can plant malwares in your storage and keep your NAS+router a part of botnets. In case of this, the abnormal behavior of your NAS+router can less likely be controlled or blocked because the infected system is actually sitting at the edge of your network!
Also, linking storage system which runs with HDDs to the router greatly increases the possibility of having downtime of your network.
Don't forget that HDDs are fragile. If the HDDs inside your NAS+router go dead, would it affect routing function of this machine?
Synology is crazy to launch this product to be honest.