You get a 1% ME bonus in an engineering complex - does not apply in other structures.
If you have (for example) a M-Set Advanced Component Manufacturing Material Efficiency 1 rig installed it will grant an additional 2% material efficiency bonus in Highsec.
In Lowsec you multiply that by 1.9 = 3.8% rig bonus
In Nullsec/Wormhole you multiply by 2.1 = 4.2% rig bonus
A T2 rig the base rig bonus is 2.4%. The security multipliers are the same so 4.56% for Lowsec and 5.04% for Nullsec plus the structure bonus.