I currently have in my possession both the X900M and a new Panasonic TM900. I'm a pretty unsophisticated user, but thought I would share my first impressions, for what they're worth.
The wider angle lens on the X900M makes a significant difference, and is a big improvement, at least for my needs (currently making videos of the construction of a new house, interiors are more easily captured).
Low light performance (using just the auto settings) seems to me to be slightly better with the X900M.
The TM900 is easier to grasp, and slightly lighter, but it is not a big difference to me. The X900M is still a very small device, compared to its competitors, and easily slipped into a jacket pocket.
The EVF on theX900M is brighter.
The eyepiece corrector dial on the X900M seems more stable. With the TM900 (and the TM700 before it), I had to adjust the dial almost every time I pulled out the eyepiece. However, the mechanism appears identical, at least externally, so this may just be a random difference between the particular units I have.
The sound recording on the X900M seems richer, based only on recording my voice as narrator.
The exterior of the TM900 is glossy black, the X900M matte black. Conceivably this would make a difference if the user was in sunlight and wanted to be unobtrusive, the X900M might be marginally less obvious.
Based on the above, I'm going to keep the X900M, and return the TM900.