Extremely fast to start on-demand, reliable and although a little bit pricy but not unreasonably so considering the alternatives.
And the DX is amazing! it's just like any other fly machine, no new set of commands to learn. Deploy, logs, metrics, everything just works out of the box.
Regarding the price: we've tried a well known cheaper alternative and every once in a while on restart inference performance was reduced by 90%. We never figured out why, but we never had any such problems on fly.
If I'm using a cheaper "Marketplace" to run our AI workloads, I'm also not really clear on who has access to our customer's data. No such issues with fly GPUs.
All that to say, fly GPUs are a game changer for us. I could wish only for lower prices and more regions, otherwise the product is already perfect.