I bought the premium version to input in real time with my midi keyboard, but the delay is frankly unusable, is there a way of fixing this?
It depends on the computer, OS, and a bunch of other factors. Every MIDI input will have a delay. They can try to compensate but all software that uses MIDI will experience it.
What you can do to minimize the problem:
First and foremost, not have a bunch of other programs running. Don’t have a lot of windows open in the browser.
I hold down the first note while the click counts down. That keeps me from trying to play catch-up and have many fewer notes that I have to manually adjust.