I have yet to try a long arm, and I'm just poking my head in here to say I sure hope you try it and come back and tell us all about it, and of course, show us your quilts, too. I suspect that after you have done this a few times you will not want to go back to using the DSM.
If you take the class, you will have learned skills that will stay with you, and that's always a good investment. You might ask if you could talk to other people who have taken the class and used the machine. I'll bet the shop will be happy to share good references. Maybe the shop owners can also give you a ball park estimate of how long it typically takes a beginner to do a quilt of a certain size.