I know Wciow, that's what I use, but when I was creating the labatory for Military, which has 8 particle effects at any given time (no worries, no noticed decrease in performance), it took over an hour to get those particles perfect, and that's with using MG's existing smoke and fire particles as a template. Lining those up perfectly to the smoke stacks is HARD, then there was getting the perfect colours and transparency, as well as the perfect number of particles...
EVERY change for that required me to open Glest, start a new game, wait a while for it to load, type "createUnit('lab',0,startLocation(0))" in the console, look at it, judge the changes I had to do, end the game, apply said changes, and repeat to see them. Must have started over 50 new games... A tool to simply allow me to see the model and update its XMLs in real time would be immensively helpful.
As well, months back, I had lots of balancing to do with units attacks, particularly those with "fast and weak" attacks. The humvee was underpowered still until the current WIP release.
However, the particle effects could potentially be added to the G3D viewer. MG's viewer supports so, but not with the model too (the most important part) and crashes a lot (apparently that feature of the viewer is very "beta").