Can I use Speedify without the VPN server?

If you want the short answer:

No. This is because in order to bond Internet connections, a server is required. This allows you to achieve better speeds and stability through Speedify. This would not be possible without the VPN server.

The longer answer, however, goes like this:

Speedify makes connections to the VPN server over each of your Internet connections and can divide traffic on a packet by packet basic among them. The VPN server is the one that provides a consistent endpoint for communicating with servers on the Internet, so those servers on the Internet always see the same public IP address for a request, no matter which of your Internet connections the packets used.

If your client device were to start sending different parts of the same request over different Internet connections without an intermediate server, namely the VPN server in this case, the servers on the Internet would get confused.

While there are routers and software products that offer load balancing across multiple Internet connections without a server, this is different from the bonding that Speedify offers. With load balancing, a single request (socket) is assigned to one Internet connection and remains there for the entire request. If the Internet connection fails, the request is broken and needs to start over with a new Internet connection.

In contrast, Speedify is able to seamlessly transition a request between multiple Internet connections without interrupting the request. This is especially useful for long-running single-socket activities, such as live streaming, video calls, file uploads, etc.