@Crafter of War - I've read the intel report on Mandate defenses. On the one hand, I can see the logic in wanting to deploy the MAWLRs against the Mandate's heavier fortresses. But on the other hand, the Mandate is currently undergoing the start of a full-scale civil war, and this should have a substantial effect on their security and military responsiveness, and we have options for further exploiting those cracks to boot. We may be in a position where we either infiltrate their fortresses with the aid of defectors or render them largely toothless by liberating the surrounding areas and besieging the remaining holdouts.
Aside from the above, I have a feeling that deploying the MAWLRs will inevitably result in a greater degree of collateral damage. AND, once the rest of the Inner Sphere gets wind that we have literal WarShips on Legs, they're going to start developing defenses and countermeasures against them. This will obviously happen at some point in the future anyway, but I'd prefer to hold off on revealing them until we're in a war with one of the Great Houses.
EDIT: This is assuming that the Great Houses don't already know about the MAWLRs. If they do then the point about 'surprise factor' is moot, though I feel that the bits about the civil war factors and collateral damage still stand.