Yes and no. The encryption and stealthing of our servers can certainly play havoc with speed tests. The best test of how well the VPN is working is to browse a bit with it, or use it for whatever reason you purchased it. Even if a speed test gives you a bad result, you may find it’s actually quite speedy in practice.
If you still wish to try, be sure to select the city closest to the VPN server you are connected to before running the speed test or the results will be horribly skewed. On Speedtest.net, this may involve you dragging the map so you can choose the actual city you’re connected through. This will still attempt to measure the speed to your computer from that city.