Research used to be handled with only green papers and resources, so the Double Gain IAP straight up doubled the speed at which you could buy research. Now that there is a third currency (blueprints), Double Gain is no longer as effective as it used to be - which is a huge slap in the face considering it's an IAP. You can sell resources to purchase chests for blueprints, but the chests are just not worth the investment and you end up coming nowhere close to buying research twice as fast as a f2p player (which was the case before the patch).