I've had some bad reactions to "fake" Apple Watch bands. Had a burn / rash on my wrist that lasted about a week. A lot of them have really bad chemical smells that never really go away. I have stuck with Apple bands and ... a year+ later, they're like new. Personal experience - I'm sure there are others that have had no problems.
But for my wife and I, we've found the 3rd party ones to last a few months or so resulting in a much more expensive band over the course of a year.
I've settled on the Sports Loop and have used one for over a year every day now.