I'm very tempted to start offering this as I have some images that I think would be perfect.

Just wondering if anyone on here has done this before and did the process run smoothly?

Thanks

You might as well give it a try.  I have sold some.  Offer the same images on other items while you're at it. 

Sometimes I sell phone covers through FineArt America.

I actually joined redbubble 10+ years ago to make a custom cover for my daughter's iPad and ended up selling phone covers there too.

Reviewing my last few years' spreadsheets quickly, sorting sales by product shows that I sell more iPhone cases, clothes, home decor, journals, greeting cards & stickers on Redbubble compared to FAA, where most sales are prints (followed by Puzzles). Obviously my profit per sale on Prints is many times higher than for other products, but my markup on home decor and phone cases still adds up nicely. Depending on the kind of case, my markup is between $6-9. Not a get rich quick item, but it adds up okay.

In terms of quality, I've purchased iPhone and Android cases from redbubble for over a dozens years now, and they have held up nicely, outliving my phone and my family's. We tend to keep our phones for about 4 years, so they are good quality. I haven't bought cases from FAA, but I've been happy with samples of various other items I've purchased there and I assume they're the same as RB.

If you want to offer cases, I'd do it soon since sales have already started picking up for the holidays. Sales of products peak every year between November and early January.