I will never take mongoose on main hand. Ever. I've put it on, replaced it several times, and i guarantee you i always outperform the duel mongoose guy. I don't care about any statistics, i've wasted about 4000g on mongoose enchants, it's crap. It's all well and good talking mean uptime figures, but what people forget is the amount of time it procs 50% and more into the battle. I always feel unhappy with mongoose, doing minutes of a battle with no proc. I put it on again recently, it took 7 minutes of constant fighting to get one proc - i have a holy paladin keeping me up and letting me zerk the field.
People always give me shit about mongoose, but i'm sticking with how i feel. I've tested it enough, and compared the damage tables enough to know that 20AGI is on a similar performance level overall to mongoose. The other problem is that it is so blatantly obvious, two swords over your head and people gtfo. How much swing time do you ACTUALLY have with mongoose running?
5 points in relentless strikes is just too many wasted points IMO. I'm sure if you compared the extra crit to the 5 points in relentless strikes, particularily over a mid to long period, crit would come out on top.
The choice for garotte is simply, i also sometimes, depending on the situation open with an ambush, but rarely. Garotte gives me another 150 on my opening (25 energy = 25/35 hemos or about 150 damage) - hit garotte and GS and you've really just damaged your hardest opponent - mage. If there is one class that is going to own you more than any other, it's the mage. Slightly sloppy play and your eating a pyro. Open with a imp GS and a garotte, you're making him sweat.
The heightened senses really should be taken, however, i ALWAYS arena with catseyes. The >20% crit makes me sleep at night. I'm going to say something really stupid now, but i do not really think anyone really, truly understands the combat mechanics of wow, and i'm tempted to say that wow will try to normalize 1 in 5, precisely, over a long time. There is something really strange about crit, that i can't fathom. The difference between 15% and 20% is enormous, anything about 25% seems wasteful. At one point i had 50% crit on my feral 80 druid, and there is no way i was critting 1 in 2 - try 1 in 4. This was against a standard mob, of same level, x parry, dodge etc, my 50% crit chance had full space on that combat table.
Even if its capped at say 40% (i do not know the exact figure) there was no way i was getting 40% crits, as i said, try 25%.
I play equal arena and BG, so AB trinket is actually more beneficial to me overall, however, with the 12 stamina changes, it is something i might go for.