Yeah, if you record a finished mix or stem onto this and then play it back you might have bad wow&flutter. Bad frequency response, lacking high end.
If the playback/record speed is inconsistent, you might find your stem being a couple seconds longer all of a sudden, when you record it back into your daw. In other words it will go in and out of tune and not match up with your project.
There is a way to (kind of) get round this, by recording and playing back at the same time using the headphone output. You would need a three head machine for that, I believe this one is a two head machine.
I have an Akai two head machine which hasn’t been serviced. So even though I got it functioning, it is not up to spec, so all it can be used for in my setup is for recording drum samples unto it to add tape saturation and the amp into the sound. Because drum samples are short, the wow&flutter problem isn’t gamebreaking.
Compare it to owning a seventies car, you have to know how to work on it for it to be a reliable driver.