Personally, I would have preferred to see Colonel Mace return, although it is nice to get a returning UNIT character at all in the new series; it harkens back to the returning UNIT characters of the 70s.
One thing that bugs me, though, is why does Magambo wear a black uniform rather than the khaki one that the other UNIT officers wear (such as Colonel Mace, Captain Price, Major Blake, and the other officers we saw in the Tower of London HQ).
Presumably, since it is worn with a beret and not a peaked cap, it is meant to be closer to the black fatigues worn by the standard UNIT troops; unfortunately, the uniform that Magambo actually wears is made from British Army ceremonial uniform, and is thusly far smarter than the standard khaki one (the British uniform code specifies it as No 1 Dress, and is equivalent to what Americans call Dress Uniform). If they wanted a black uniform for UNIT officers, why not just put them in a black military jumper!
See my sketch below for how it could look - complete with a black 'norgie' top and black combat trousers...
Alterantively, if they like the idea of keeping officers in a shirt and tie, there is a V-neck jumper available...
Perhaps I shouldn’t get so irked by something as insignificant as costuming details!!
