When I bought my first chin, she had a chin spin and she LOVEEEEDDDD it. She would really fly on that thing! She slept in it, ate in it, lay on her side and rocked in it, she just adored it. It's great because it takes up way less horizontal space (about 5 inches or so by 15 inches). Chins also pick it up really quickly. The only thing that I hated was that it shook my cage like crazy. No one in the house could sleep at night. I had a lot of trouble stabilizing my cage and trying to quiet it down. It was a QC, so it wasn't a rickety cage either.
When I got a 2nd chin and moved them both into a new QC Townhome, I got a flying saucer. Right off the bat you'll notice it takes up wayyy more cage space (about a square foot, plus a couple extra inches on each side). My first chin that used the chin spin all her life picked it up like nothing. Within hours she was flying. But the second chin who was only 3 months old and wasn't partial to a chin spin didn't pick it up as quickly. She just started running on it today! It took her about a month. For me, the saucer is quieter and easier to stabilize than the CS. You have to assemble it though. The chin spin just hooks onto the cage. I love how much less noisy the saucer is, but it takes up so much more cage space, and I know my first chin misses her chin spin dearly cause she can't lay down and stretch out on the saucer. But because it is so much quieter for me and the chins are in my bedroom, I'll be sticking with the saucer for now.