I wouldn't buy an SE right now unless you can get a very good deal on one - those things are getting old and there may be an SE2 to replace it sans button coming soon.
The SE is performing solid on iOS 11. The A9 really isn’t that dated of a Processor. As for the SE 2, highly questionable if that will happen or not. I’m hoping it does launch somewhere in March with a spring Keynote. If it does, I think it will retain the home button.