My first ever experience with flexible filament, back in March 2021, and it went much better than I feared. AzureFilm's Neon Orange TPU is squishy, practically indestructible and surprisingly easy to print, as long as your bed is perfectly level.
The one thing that matters: bed levelling
As usual with AzureFilm (made in Sežana, Slovenia), the spool came vacuum sealed and wound very neatly, which not every brand does. My first calibration cube came out great. Then I got cocky. My bed wasn't levelled perfectly, and the next prints (wristbands and cable clips) all failed.
With TPU it doesn't matter much whether the bed is heated. What matters is that it's perfectly level, with the nozzle a little closer ("more squished") than for regular PLA. Once I fixed that, everything worked. The CaliCat came out smooth with a bit of stringing on the ears, which I cut off, and a bowl with a little support was a bit rough underneath but easy to print.
Squishy tabletops
TPU is about 90% for useful stuff, but I couldn't resist. The MatterHackers filament astronaut, all TPU at 20% infill, is squishy and I'm in love with it. A flexible octopus at 20% infill, no raft, no brim, straight on the bed: the kids love it and it's unbreakable.
Vase mode took a few attempts. The first failed, the second had walls that were too thin and started breaking as I squeezed it. At 0.8 mm line width the result was soft and fun. Over-extruding to 0.8 on a 0.4 nozzle works about 80% of the time, but with TPU, especially if you go too fast, it doesn't always.
Where TPU shines
I printed tyres for a Tesla Cybertruck model. I still used 40–50% infill, they would be softer at 10%, but they look great. Then I printed some simple cable bands with a hook: practically indestructible, and I planned to print 10 or 15 to tame the mess behind my computer. Finally, stick covers for my DJI Mavic Pro controller, so the flimsy sticks don't bend in my backpack.
After trying up to 250 °C, I settled at 220 °C (AzureFilm suggests 200–230 °C). Apart from levelling, that was the only thing I had to tune.