Fly with them for sure
Haven't been here for a while, hope everyone is well.
What IDPASteyr said. I've traveled to visit the inlaws in AZ and to a few matches around the country with guns. It is really easy and like IDPASteyr said the law is there are no markings indicating a gun, the TSA tags are inside your locked case. I put my pistol cases inside of another piece of luggage with TSA-approved locks and it only adds about 2 minutes to the check-in process.
Other passengers will look at you funny when you are at the counter because you have to open the case to show the guns to the check-in agent to show they are empty (at least with Southwest Airlines). Another important tip with Southwest Airlines is that the ammo must be carried in boxes designed to transport ammo - like original factory packaging or plastic ammo boxes. Ammo cannot be stored loose. I was in AZ and bought a bunch of Sellier & Bellot at J&G for a song and didn't shoot it all. What was left of a case I put into a heavy-duty Ziploc and had to "donate" it to the airlines when they inspected it. The rest of the ammo that was boxed was just fine.
Separately, I too have strayed from my Steyrs. I got really into IDPA and IPSC gaming and broke down and bought a Glock 34 (5.5 inch 9mm with extended mag release and safety). Interestingly, it has taken me much longer than expected to adapt to the Glock. It really feels like it has a significantly more muzzle flip compared to the M9 and at first my pairs were wild. It feels like the slide mass is twice as great as the Steyr and takes twice as long to cycle. I find I really have to be locked out to get consistently close pairs as fast as with the Steyr. At longer ranges (20 yards +) however, there is no comparison as the longer sight radius and Dawson Fiber Optic Front/Blank Adjustable Rear sights make the Glock 34 super-accurate. A $50 trigger job still isn't as good as the Steyr, although it is lighter.
In summary, I think for up close and personal ultra-fast shooting, the Steyr design (ultra-low bore axis, short slide and steeper grip angle) is nearly impossible to beat. An M9 and S9 will still be my carry guns. I'm looking for some night sights, however.