The 4X5 retaining panels are mostly designed to prevent the sheets of rolling off the reel during high speed rotation.
In the past 10 years of using 2509 reels i have never used the panels (older reels did not have them, and as a habit my newer ones dident either...). I have never seen a sheet dislodged in any process i have run, manual or machine.
Inversion is totally possible with the multitank 2, but uses as noted above almost 1.3 Liters of chemistry. If that amount works for you with dilution or stock there is no reason not to do that, and many schools around the world teach that system of processing using the 2520 system tank.