I also have and use Mark of Norgannon quite often when I need a TPS boost, works very nicely, even though I too was a bit meh about the haste effect at first. Depending on the encounter, I often swap it on just for a little boosted threat, or in some cases where I want to max out, I'll toss on both MoN and Grim Toll, which allows me to get to both the expertise (parry) and hit caps if so obliged. Pulled 3116 DPS on patchwerk while tanking 2 weeks ago using this set up, and I didn't even have any DPS consumables on, and likely may have at least been missing one or two beneficial buffs/debuffs. Was sort've just doing a test run, going to aim for more and maximize more toward higher TPS/DPS on Patch specifically in the future and see how that goes.
Anyway, gl to all with getting your hands on it, I've found it to be pretty useful so far.