I have had next to no Latin experience (Latina Christiana 1&2 only).
I bought the Comprehensive Guide. Honestly, I think I have cracked it open twice this year. I find really doing-really doing- the workbook has been the biggest help in solidifying the info. Even when we(my girls and I) have not initially understood what we were doing in the workbook, as we stuck to it, it became much more clear. If I had it to do over, I would not have purchased it. my < $.02
hth