Attack-capable mechadendrites allow for an attack as a reaction, and the Weapon MIU allows a linked weapon to be fired as a free action. This raises a series of questions.

With the weapon MIU, can the character make a full attack action such as suppressing fire as a free action? With a ballistic dendrite capable of semi-auto fire, can a character use suppressive fire as a reaction?

Can dendrites and integrated weapons be used as secondary attacks with the Two-Weapon Wielding talent? If so, what would be the resultant penalties? In this way, would it be possible to attack with a two handed weapon, then a dendrite per Two-Weapon Wielding, then a separate dendrite as a Reaction?

Can a dendrite's reaction attack be made in addition to any other attack actions? I'm thinking the dendrite attack would have the Attack subtype, (thus being exclusive with any other attacks in the round) regardless of being a Reaction.

You cannot make two actions with the attack subtype within the same round unless something specifies otherwise.

Suppressive Fire is quite a specific full round action.

I'd allow dendrites to be used to dual wield, but still only making two attacks - one with each specified weapon.

Re-read the Using Actions section on page 242 of the basic rules and I got an answer on part of this. The 'one attack subtype' limitation applies to the turn, not the round. A reaction with the attack subtype can be used in the same round that an attack action is made.