I am switching because after almost 4.5 years on Tasigna, 3.5 years of which have been on the current low dose, I still have a number of side effects including ectopic heart beats (these resolved when I tried TFR this past summer so I know it's the Tasigna), mild dry mouth, and more recently the progression of peripheral neuropathy from stage 1 to stage 2. Stage 1 started about 1.5 years into treatment with Tasigna. Since I have none of the other causes of peripheral neuropathy, I'm pretty sure it's the Tasigna that's causing it.
If my side effects are worse on Sprycel and/or if I lose response, I will switch back to Tasigna.
I would never consider switching just because of the fasting protocol. I have been able to manage around that fairly easily. Nevertheless, you should discuss that with your doc.