I personally like the idea of engineering borgs being able to have circuits on them. In particular I like the idea of a "circuit storage pouch" that was mentioned above. I think that, just like playing a physical engineer, it should require intentional preparation.
A humanoid engineer can be unprepared if they don't fill a box with things they might need before heading to a job site.
If a borg always was just printing or generating circuits then they would have a clear, unarguable advantage because they would ALWAYS be prepared without putting any effort in that the humanoid engineer has to put in.
If, however (like was suggested), the borg instead has to also do the same type of preparation that a humanoid engineer would do and have to fill their own box of circuits, have a limited amount they can hold, etc. Then this doesn't give them any sort of advantage over regular engineers and there would still likely be just as many borgs who don't bother doing the prep as there are human engineers that don't bother with the prep.
I think however that this circuit carrying case should be limited to "standard" boards like the following:
APC board
Airlock electronics board
Air alarm board
Fire alarm board
(probably some other basics that I'm missing)
This would mean that they can't (and shouldn't be able to) just stock up on every type of circuit board you can print in RnD just in case they need it. Those types of boards they can still carry one at a time in their gripper to install as needed but they can't have a huge stock of them hidden away inside them or anything.
I see this more as a quality of life change rather than a buff. Engineer borgs are still limited in a lot of ways such as being unable to use plasteel, being unable to move things around with hands, etc. I don't think this change would make engineering borgs any BETTER than they are already, all it does is make it so they don't need to drag a silly locker around to accomplish the same thing that they already can.