it is possible to use 2 at one time, except it isn't a real time stompbox-esque chaining of 2 effects. rather you have to set presets to include the effects you want, with parameters and everything set. it is possible to modify parameters on-the-fly with an expression pedal, but to assign the knobs kinda limits your sound.
for instance, if i wish to have a flanger and trem in one, i have to create a new preset, assign flanger to preset, set desired characteristics of flanger (wave shape etc), assign parameters to be controlled for flanger to exp pedal/MIDI, repeat for trem. the end result is a flanger/trem that can perhaps have its speed modified on the fly.
if you are looking for a particular sound, there is none better however. the insane number of tweakable parameters and settings allows you to nail any modulation you might have in mind. /advertisement over. I used it as a replacement for ALL of my modulation pedals, which knocked pedals such as my deluxe electric mistress right off the board. in fact, the only reason I sold it was because I was replacing my entire pedalboard setup with a g-system, which would hopefully simplify everything. (now that i'm looking at wiring diagrams, i doubt that)
edit: j_m_s, you can use it with a 1spot, but the current draw is 1200ma, which does not leave much for your other pedals. 2 eventides? not much diff anymore.