In my opinion, instructing is a great job, other than a great experience, for those who really want it.
I had loads of FIs really passionate about their job, and some others not.
useless to say that flying with the latter has been as hassle.
In other words do it if you really like it.
Anyway I'm still not 100% convinced if airlines are interested in extra 500h on piston aircrafts, rather than hours on type.