Pimsleur Chinese is excellent, but it takes patience to get into it, especially if you know a little bit already. There's a spaced repetition schedule, and you're not aligned when you start. Caveats:

1) You don't see spaced repetition working until a few weeks in, once you're on a schedule.

2) You can't have gaps, so you can't just start in the middle.

3) If you know stuff, you need to keep with it until it gets into new stuff.

From there, it has to be done daily. If you miss 2-3 days, it's a chore to get back onto the schedule. I did it when I had a commute, so investing 30 minutes per day was easy. It added no time to my day, and by the end of 3 months, I knew /a lot/ of Chinese for not a lot of time invested. I was on-par with people who had roughly 2 years of college classes for speaking (but not reading or writing, which Pimsleur doesn't touch on). My accent was better too.

Once I finished, there was nowhere to go. Nothing else was nearly as efficient. I kind of plateaued. There are better tools now; this was many years ago.

I did the library/CDs route, so it was free.

I highly recommend the same path.

I haven't found anything good for writing Chinese. Does anyone have recommendations? Ideally, it'd leverage a pen tablet or iPad pencil or similar.