Couldn't find the amazon link to that slicer.I've not been to Tuckers, nor bought an onion burger in a while. We got a little joint on this side of town called Old Time Diner that makes a good onion burger.
But yours look better.
Kosmos Q worked in an onion burger joint in El Reno, when he was in high school, here's his version, and oh yeah, the mandolin onion slicer he recommends is a good one.
https://youtu.be/WHDVxnBQ8xA
Looks quality and multi-functional.This is the slicer I have. Sharp as hell, four different thicknesses to choose from.
https://www.amazon.com/Swissmar-Borner-Power-Mandoline-V-7000/dp/B003DZ0BRG/
Now considering a better mandolin. The cheapo I got at BB&B scares the hell out of me. Feel like I could end up in the ER anytime I use it.
Kinda like this one on Amazon with the container and protective glove.