I've had, or now have various types of inserts. I have settled on the Kreighoff shotgun barrel insert in 22mag. It is sufficiently accurate and Hits with a bit of authority. Ammo is inexpensive and easy to carry. A gunsmith familiar with drillings can alter the flip up sight to stay up with the rifle barrel de-selected, so you can use the right barrel with the insert, the rear sight, and the set trigger.

My inserts are all the longer rimfire type, about 12" or so. The shorter barrel inserts are far better to carry in the field, however, and I may have mine bobbed about 4-5".

The full length inserts in centerfire calibers are accurate, but are also not as convenient if you want to use both shotgun barrels frequently during the hunt. I got rid of mine in 22 Hornet and 222 Rem for that reason.