It basically gives you sanctuary when you use it by itself for about 4 ticks and has a 24 tick cooldown.

If you stalk your victim many times before you trance you can expect the same effects of a fully charges Striking the Shadows Footfall warrior.

I use it over assassinate because at best assassinate is a 50% chance to kill someone and often times martial trance is just situationally better. (For example if I'm being raided by a group of 3 as a solo defender I will stalk and trance instead of assassinate 1 and lose my item anyway)

All of the helpfiles for the various trance Buki edges are pretty self explanatory though I have no idea why anyone would forego the 300 hp edge when tranced over any other one. (It's really about 600 hp because of the sanctuary effect damage reduction).