If you just pay the tax it goes into general revenue. The people of Manono may never benefit, the money going to more football fields in Kinshasha or something else. The people of Manono may never have a vested interest in the success of the project and may miss out of the benefits.
If you do a SEZ, its directly targeted around the region. The incentive to have a positive relationship is now two way. Workers get trained, kids get schooled, power improves, roads get better, health gets looked after.The leaders in Manono also get input in and therefore feel they have some result from what they'll be doing with AVZ and will more readily support more growth when CDL becomes real or we bump up production capacity.
AVZ becomes more bankable. Lower cost to produce/ship, offsetting higher transport costs.
All attributable to the big hole in the ground on the outskirts of town.
SEZ is a win/win/win, For AVZ, for Manono, For DRC as a whole . General taxation, not so much, maybe only DRC.