I think a bit on connectivity terminology and has nothing to do with file access and sharing
Remote access, for many in IT, is used to refer to remote users (roaming on the Internet or other non-home/office location) gaining access to the home/office LAN as if they were on the LAN. Typically this is achieved by running a VPN server within the LAN and users use VPN client to login and create a secure tunnel. The VPN client will be either built into the device OS (most support L2TP/IPsec VPN) or an add-on app (e.g. OpenVPN). You'd open firewall ports to allow direct incoming VPN requests to the VPN server.
QuickConnect (QC) is a mechanism provided by Synology that aims to make it easier to access the NAS from wherever you are and however you've configured your Internet firewall. QC will determine the best connectivity method and handover to that:
- Test confirms client is on NAS's LAN: direct connection between client and NAS
- Test confirms client is on the Internet but DNS resolves to home/office (or direct IP) and firewall port forwarding is setup for to the NAS for this service: client will directly connect to the NAS
- Tests confirm that no direct access is possible but NAS has QC Relay enabled:
- NAS creates outbound connection to QC Relay.
- QC replies to client to send traffic to QC name address (selected by you in the NAS).
- QC Relay acts as a proxy to pass packets:
- Client -> QC Relay -> NAS
- NAS -> QC Relay -> Client
To use QC: instead of entering a direct DDNS/DNS/IP name in the web browser or mobile app what you enter is the QC URL or QC name (depends what app you are using as to whether just the QC name will work) plus port number (sometimes).
But in the traditional sense QC is not Remote Access it's just access to NAS services and anyone on the Internet will have at least the ability to get to the NAS service's login page, provided they know your QC name, so use strong passwords. Whereas Remote Access is an additional layer of protection that the user authenticates to and that then allows access to LAN services.
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So the question is: Do you want Remote Access or normal access (whether gained by direct connection or QC Relay)?
To enable Remote Access you use DSM's VPN Server package to setup OpenVPN and/or L2TP/IPsec VPN servers (PPTP VPN is considered too weak so don't use it). You will then configure your Internet firewall (and DSM firewall) to permit inbound connections for the various ports needed and send them to the NAS. Within DSM you can setup and maintain a dynamic DNS (DDNS) that will track your Internet IP that your ISP gives you.
Similarly, to enable direct access to whichever DSM services you enable you would do the same to configure your Internet and DSM firewalls and setup a DDNS.
If you don't want to do direct access then QC Relay will be the option. Set this up in DSM too. Be aware that while the client and NAS will make secure HTTPS connections to the QC Relay there is no guarantee that traffic across the relay is secure or, at least, not accessed by anyone ... other than Synology's word. QC Relay is in effect a man-in-the-middle: I don't see where they've said that the technology tunnels actual data through a second SSL wrapper so that the outer wrapper is used to manage routing between client, relay, and NAS.
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Once you've established the connectivity methods you want to use you can then decide what file and media services you want to use: File Station, Drive, Audio Station, Video Station, Moments, Photo Station, (DSM 7's, when it's released Photos), Plex, SFTP, WebDAV.
Plex Pass gives you access to managing multiple users, but take a look at the Synology Audio/Video/Photo Stations and Moments which all have user management built-in. Specifically look at Audio Station as this (for me) offers better external speaker connectivity than Plex. You don't have to make a decision now as you can run all these packages at the same time and with the same media files (personal media in home folders can't be shared with Plex). You can then decide what's best for you.