Any experiences with Printdoors tumblers and their profit potential?

[Dabou]

I found this Classic Outdoor Tumbler (540ml/18oz) | Stainless Steel 304 on Printdoors for $6.96 plus $13.20 express shipping (takes 7-12 days). That shipping time seems alright to me. If I set the price at $40, I could make $19.84 per sale, not counting all the fees. They seem like good quality, so I reckon they'll sell well at that price.

I've looked into Printdoors, and some folks say they've used them with no issues. But I'm still unsure about the quality of the tumbler printing. Anyone got experience with them, especially with tumblers or other products? Any experiences to share?

Where do you get your tumblers, and what kind of profit do you make on them? Know of any other places where I could find them at a decent price to ensure a good profit per sale?