I do use a Trash Panda Quad for switchable expression, with active control over each output.  I can’t speak to the Saturnworks, but it’s of a passive design (power required only for the LEDs).  I don’t know how well the H90 will react to that, regarding calibration, potential for voltage division, etc.

This quote bothered me a little, as it’s contradicts the H90 spec:

Expression pedals fall into two broad categories: the more common TRS (stereo) configuration and less common TS (mono) configuration. EHX, Boss, Dunlop, Strymon, Moog, and many others use TRS. A handful of brands, including Line 6 and Eventide, use TS.

EXP/CTL

Two ¼” tip/ring/sleeve input jacks for a variety of parameter mapping and assignment options. Accepts the following:

10-25 K expression pedals.

As did this one:

Please note: The controller is designed to only have one device active at a time. Having more than one device switched on at the same time may cause the device(s) to malfunction.

Saturnworks devices are very configurable, pre-purchase.  I’d contact them directly, and perhaps Eventide or another end user can chime in here on the specifics.