Guitar Trainers(Worth the Cash?)

Title says it all rele, Ive been looking into buying a guitar trainer, you know the things that u put any of ur cds in and it removes the lyrics and u can slow it down and what not to get solos and stuff down. I think it might be a good idea to invest in one as soon as i get a better amp + guitar as soon as i start getting paid. Anyone have one or have used one?

I've thought of one those myself but i came to this conclusion. The main thing is recording yourself to see where your errors are. So in my opinion you are better off buying a digital recording device and record your playing and listen to it.