From someone who has had the dimmer model for the last almost 2 years and has a couple of the new Z wave plus models I can say that there is no delay when physically turning them on and off. There’s almost no delay when turning them on via the app or through Alexa or whatever other method. There is a ramp up and down that may take a little longer to get to full brightness but for me its acceptable. I have used custom device type handlers to tweak those ramp rates and then once it was done I switch back to the default handler so it would run locally.
I will saw that there definitely is a delay between physically pressing the button and seeing the change within smart things, it can be anywhere from 2 to 6 seconds. But as long as the lights are turning on and off I really don’t need instantaneous status update within the app, I rarely use the app anymore and try to use Alexa for most things.
I have had some weird compatibility issues with different bulbs in the difference between the Z wave plus and nonplus affected bulbs differently. In general my can downlights, no matter what brand, always worked fine. However I have had problems with candelabra bulbs within my ceiling fan lights. The non Z wave plus version combined with Cree candelabra bulbs result in the bulbs not turning on about one out of every 5 or 6 times while the switch was actually on. I’d have to turn the switch off wait a few seconds and turn it on and then it usually worked although a couple times I’d have to do it a 3rd time. I switched most of my candelabra bulbs over to a philips warm glow and they seemed much better, have the problem about once out every 15 times. Switch to the zwave plus version and the problem mostly went away BUT now they have to be above about a 15% minimum which is wierd because i didnt have that issue with the non-plus switch.
If they made more candelabra bulbs out there I would try another brand but that segment doesn’t seem to have a whole lot of selection. Over all I still like the GE switches the best and every once while you can get them on sale at lowes and combine it with a coupon and end up being around $30 a switch.