We always used sterile water as well and never had any outbreaks. The problem, from what respiratory told us, is that the internal filter cartridge wasn't disposable and there wasn't a way to sterilze it - therefore between patients you couldn't really clean the units out completely.
I am pleased to hear that they're coming back, but we won't be getting them. After the recall, our unit bought a bunch of the Fisher Paykel versions so we would lose money if we got rid of them to buy or rent the new Vapotherms. I haven't noticed much difference between them except that the FP versions don't have alarms on them, so you don't know if your baby is disconnected somewhere along the tubing.