Ever since the rocket boots became the rocket belt, and on occasion fatal, I've struggled to find a decent tinker for my belt slot.
After some bad out of raid experience with the shield's "aoe taunt" failure chance I was content with the "cardboard assassin" and it has come in handy in tier 11 on some fights where add control was dicey (well, I survived to reset instead of nasty repairs anyway)
The belt tinker is a toy, few provide any real advantage in a raid, or if they do come with some pretty wipey failure scenarios, the shield and boost are dangerous, the invisibilty can be useful for sneaking past mobs while soloing, the Mind control is quite fun in world pvp and unrated BGs.
I always use the nitro boosts..."sometimes fatal" is why you have healers...I found them particularly useful on Rag (as melee it was sometimes sketchy to get to my son of flame without them). The only other one that might be useful in a raid is the shield...I use that as resto if I need a moment to not worry about myself and just heal up the raid.
Worrying about the failures is pointless, in my experience.
Or as a DPS, aoe taunt mid-fight... yea. Guess I'll go back to testing on the Cardboard Assassin... I'd hate to be the guy, "...would have gotten a realm first but for that one engineering backfire"
As to invis: Am Hunter. /use Camoflauge
Mind control: Blizzard does nasty things with MC hunters.
Nitro ka-blooie: Self-heal? what self-heal? And wtf, you healed the tank instead?
Mass taunt/CRIT-ME-BABY/Stun: Hunter. If I need to "tank" its with my Mr. Fuzzy or by having aggro and running like hades.
Cardboard Assassin: worst thing I've seen so far was a random ninja cutout waving us bye bye as we wipe. Best was it holding hm Magmaw parasites while the kiter got Rebirthed. Still wiped but was epic fun.