These calculations reflect the contributions of 'ordinary' Ogres (ostensibly costing as much as the Tenderiser) to Combat Resolution (CR) over that of the Tenderiser itself. Note that for the purposes of this example, it is assumed that the Tenderiser's multi-wound ability comes into play.The Calculations
[Ogre type] with [equipment] and 1 rank behind him (+1S impact hit) charges into T(x,y,z) unit. Damage before factoring armour = A. Assume 4+ to hit in combat in all examples (note that this is somewhat conservative - a Tyrant will often be hitting on a 3+).
Ogre Bull with nothing but a lowly an Ogre club charges. 1 S5 impact hit, 1.5 S4 -2 Sv hits. Against T3, 4 and 5 will do 1.8, 1.4 and 1.0 wounds at -2 Sv, respectively.
Ogre Bull with AHW or Ironfist charges. 1 S5 impact hit, 2 S4 -1 Sv hits. Against T3, 4 and 5 will do 2.2, 1.7 and 1.2 wounds, but some will be at -1 Sv (which potentially means fewer casualties than an Ogre Bull with a club).
Irongut charges. 1 S5 impact hit, 1.5 S6 hits. Against T3, 4 and 5 does 2.1, 1.9 and 1.5 wounds, some at -3 Sv.
Tyrant with Tenderizer charges. Assume 4+ to hit (again, as a worst case scenario). 1 S6 impact hit, 2.5 S7 hits. Against T3, 4 and 5 will do either 2.9, 2.9 and 2.8 wounds (some at -3 Sv, some at -4 Sv) against single-wound opponents, which turn into 2.9-7.2, 2.9-7.2 and 2.8-6.9 wounds against multi-wound opponents or in challenges (average - 5.1, 5.1 and 4.9).
If used on multi-wound models (e.g. Minotaurs) or in challenges, the Tenderizer will provide (on average) +2.2 CR over a simple GW (or a Bull/Irongut). That's using worst-case 4+ to hit. What this means is that for the cost of one Ogre Bull you get to drop an average of +2.2 CR, and potentially as much as +3.3 CR, onto a hapless multi-wound and/or 'championed' opponent. Alternatively, when fighting a Shaggoth/Dragon the Tenderizer will allow your front rank to actually kill it rather than just wound the thing (and receive attacks back). So does that make the Tenderiser worth it? Well, from my experience there aren't that many champions or multi-wound critters running around the Tournaments in which I play (and those that are could potentially try to avoid fighting your Tyrant altogether). Conversely, a savvy opponent would try to throw his nastiest critter or character at your Tyrant, which is where the Tenderiser shines. And then, you could always run into other Ogres, Minotaurs, or some silly Bretonnians.Conclusion
If you have the points, and don't have another magic item setup in mind, I say the potential +2.2 CR is probably worth the +36 points over a regular GW. Mainly for affording the Tyrant additional flexibility (and allowing him to survive contact with multi-wound critters without overly exerting himself).