This is an excellent article written by IGMB member "Reichsiege" about the Master of Ordinance. (I've cut out the point cost of the Advisor so I don't get sued)
"I know that a lot of you have been talking about the Ordinance guru as if he was some gimmicky upgrade that has little use or is a waste of points, but I have found him to be of great use to me and he can be a lot of fun.
As a CENSORD point model he is almost a [fourth] the cost of a Basilisk, a very powerful piece of artillery that I know many of you use. However, the Basilisk's main weakness is its vulnerability. The MoO on the other hand can be much harder to kill then a simple Basilisk. Simply loaded inside of a stationary Chimera he not only get the protection of a vehicle, it also gives him a pretty good LOS on the surrounding area. Add, a bodyguard to his unit and thats a wound that you can toss away, further prolonging his usefulness. How many times has your dreaded Basilisk been popped on turn 1 before it can even fire a shot? Our Ordinance buddy can get off 2, 3 or even more shots before he is killed, and he won't even be a prime target on the field.
Many of you have pointed out his lack of accuracy, I.E., his always scatter rule. Well gents, if you haven't noticed already, blasts weapons tend to scatter anyways. His BS 4 really tends to real in his misses and I've had multiple turns were he has hit dead on due to rolling 4 or less on the scatter dice. Also, what does it matter that he tends to scatter? He is firing a S9 Ap3 LARGE BLAST template, and it doesn't matter where it lands on the field, something is going to die.
Now comes the real kicker. Do you guys know what the Multiple Barrage rule is? This really blast our buddy into the stratosphere. By adding a mortar into the command squad, you can use your mortar as a so-called "tracer" for the Ordinance shot. After the mortar hits, all other Barrage blasts from the squad can not scatter away from contact with the original explosion, turning a maximum of 18" scatter weapon into a bullseye almost every time.
And finally, "Bring it Down". If your commander calls this order on his own squad, our little scatterbrained artilleryman gets to RE-ROLL his shots!!! (when fired at MC or vehicles of course) How can it get better then that? Combine all of these and you will have one of the deadliest (and cheapest) basilisk in the guard.
I have personally wiped out, in 1 game, with the Master of the Ordinance: 1 Wraithlord, 1 Farseer, 14 Dire Avengers, and 3 Tau Crisis suits. How is that for such a wimpy model?
*Explanation for the Tau casualties* And the fun part? Since your command squad is probably not gonna be firing any other weapons from its hiding place, you can blast at who-ever you feel like. In my game, once the enemy was too close to continue bombardment, I fired him at some Tau player's table (Don't worry, the filthy Xenos deserved it). Due to its "infinite" range, you don't even have to fire at your own table if you don't want to.
*WARNING* Firing onto tables which also contain ordinance is a bad thing , also, Tau players will sometimes get a little miffed that you shot them and outflank their entire Kroot force 3 boards down just to appear on your table, not a good thing *."
There you guy guys, now go blow stuff up!