The Dark Mechanum, is roughly the same size at the Adeptus Mechanus in real terms. They have members who are also not bound by the same rules (they will use AI) and more of them are willing to really develop technology rather than just horde knowledge, and are also bolstered by new blood who find the ADMech to restrictive. While they don't have the same number of forge worlds they are not supporting a empire the same size and only really produce military equipment from Ships to Bolter shells.
For example, from the most basic Data Slate to the most advanced warship in the Imperium the AD Mech make it this includes, Farm equipment, Medical equipment, Weaving machines etc are all made by them.
But the DM only have to build weapons of war from the most basic bolt shell, right up to Warships and they have more knowledge available to them and are not scared about disassembling working tech to learn how to make copy's of it.
For example in Priests of Mars, the Arch Mechanum takes damage to a single Capacitor and loses 30% of available power, and the Senior Magos laments the imperium and mechanum no longer have the skills to remake them, and the mechanum as a whole isn't aware the same ship has a weapon inbuilt on it's hull that has a kilometre long barrel or the true extent of the ships own database, hell they didn't even know the ship not only has been launched but has 7 names one by each of the crews / owners of the ship.
This is just from one book and a single ship that is 600KM long and fully crewed with what passes for Scientists and Engineers who are bound by rules that over 10 thousand years have turned into unbreakable religious dogma, a dogma that the dark mechanics is not bound by.
Edit, Oh an Alphadrop I am a IG player from the 2nd edition onwards and from experience they are bullet magnets, use them as needed and keep them covered until you need them or you will lose them and lose them fast. Give them Air and Armour cover i.e. a Hydra (Air and Infantry) and a couple of Russ.