Serum is a well known and powerful synth by Xfer.
Not every parameter is MPE friendly (yet ?) :
The effects of the FX tab are not MPE.
LFOs are MPE.
Vital is a powerful free synth with some similarities with Serum.
To use it in MPE, go to the advanced tab and click on MPE enabled in the left bottom corner.Don’t forget to enable MPE in your DAW if necessary (On Ableton : first in MIDI preferences for the Erae Touch, second with a right click on the plugin => Enable MPE Mode)
The effects of the effects tab are not MPE.
LFOs are not MPE.