This is a VPN client app for a SPECIFIC VPN service called 'VPN Client'. If the software works with other VPN services, fine. But I'd tend to stick with the software provided by individual services as they typically include their own features that may be useful.
The 'VPN Client' VPN service provides 7 days free, then you pay. The costs are listed at their home page. The feature list looks good, particularly "No logging of your data", which should be a requirement of ANY VPN service you use.
Problem: Where are they located? WHOIS lists nothing but their certificate authority provider. Their website offers no indication of their country of origin or address. That's a major concern these days as many governments are now demanding Man-In-The-Middle access to VPN services for surveillance purposes. That means violating your privacy rights. Example: China. I'd include Hong Kong. Using their approved VPN services would worry me.
IOW: Be choosy which VPN service you use. 'VPN Client' looks much better on the surface than many others. But concern remains.