I use this combination. I was hesitant to pay extra money to sync since the treo comes with free sync software, but since I've been using I feel my purchase was a good one. These are the things that are useful to me:
- Since I use iCal & Addressbook to sync with, I have no use for the Palm Desktop.
- I like the Missing Sync interface - nice and simple.
- I like the bluetooth sync; simple to set up and it works fine for me (kinda slow, but I assume that's a limitation of bluetooth).
- Missing Sync software lets me use my 1 GB SD card as temporary storage (mounts on my desktop like a flash drive). It's probably slower than a flash drive, but I don't know for sure, and I don't use it often enough to care.
- The license you buy lets you use it on 2 computers, so I use it at work too.
- Nice instructions are included to show you how to use it with iTunes & iPhoto.
It could be improved by letting me sync categories (which might not be missing sync's fault).
And I'm really pleased with the 650!