From a US perspective, I have about 6 of the A19 bulbs running. They are all paired directly to my ST hub. I’ve never had any real issues with mine aside from not responding once or twice. As long as you use the IKEA device handler, it’s a fairly painless process. This is the device handler that I use: [UPDATE] IKEA Trådfri Bulb Device Type
To be fair, there are some people who have an absolute HORRIBLE time pairing them to ST, but overall, I think most people say they pair fairly easily and work reliably.
AFAIK, you cannot use the IKEA gateway with ST and the remotes and dimmers are a bit flakey as well.