I added the L-1 tuner to my rack a couple weeks ago and can't believe I lived this long without it. Really helps that I can keep two different oscillators connected to it while I pass their signal on. I find it really useful to monitor my analog oscillators with the flip of a switch and confirm whether they are still in tune or need a little adjustment.
It's also nice that it offers different types of tuning so you can also tune external signals with it too, which is a big part of my setup.
I was using a tuner app on my phone before this, and the mic on my phone just made it really unreliable.