This is with new numbers and bonuses:

A)
2 x Complex Reactive
66 hp, 1% speed penalty, 2 hp/s repair @ 36 CPU 16 PG
=
132 hp, 2% speed penalty, 4 hp/s @ 72 CPU 32 PG

B)
1 Enhanced Plate
117 hp, 3% speed penalty @ 20 CPU 6 PG
&
1 Enhanced Armor repairer
3.45 hp/s @ 35 CPU 5 PG
=
117 hp, 3% speed penalty, 3.45 hp/s 55 CPU 11 PG

A.----vs.----B.
132 vs. 117 hp
2% vs. 3% speed penalty
4 vs. 3.45 hp/s repair
72 vs. 55 CPU
32 vs. 11 PG

Results?
Reactive plates give you 15 more hp, 1% faster move speed, and 0.15 more repair at a cost of 17 more CPU and 21 more PG.

For reference the total PG of a MLT Gallente Frame is 25 PG; so, just the surplus PG needed to operate the plates is about the same as the entire PG allotment on a MLT suit.

How popular would a low slot module that gives 15 hp, 0.15 repair, and subtracts 1% from move penalty be at 17 CPU 21 PG I wonder?

Sort of... it gets better:

SP cost:
A) requires Armor Plating 5
Total: 932,760 SP

B) requires Armor Plating 3 and Armor Repair Systems 3
cost 205,200 SP x 2
Total: 410,400 SP

You get:
15 more hp, 1% faster move speed, and 0.15 more repair at a cost of 17 more CPU and 21 more PG
AFTER you spend 522,360 MORE SP. You have to spend over twice as much SP for plates that are notably worse than these ADV modules.