The Bambu Lab 4-in-1 PTFE adapter makes it easier to use external filaments. You can manually load them in the adapter making it quicker and easier to swap filaments. This is particularly true if you are using the AMS as it means you do not have to disconnect the AMS to use an external filament. Instead you connect the AMS as one of the four inputs, leaving you three others for external filaments.
Using 50 mm PTFE tubing (same as I’d used for AMS feed protectors) was insufficient. Every time I got feed problems - which seems strange to me, but the evidence bore it out as true. My setup was such that I tried running a longer tube all the way to my main external spooling area, which was actually about 250 mm of tube, and this worked much better. My best guess is there’s less friction, though the drying box I am generally using for the external filament isn’t exactly friction free itself and I think adds more friction that anything else it may have brushed past.