Mods are a pure and simple lame scam.
They have an abysmal drop rate and when you see one drop it has a good chance to not be at maximum level from the challenge. If you manage to get a tier 5 Mod then most likely it will be grey, or it will be a left slots Mods or will come up with a useless primary stats. Personally, I have not seen more than 1 Mod worth leveling in a month, spending all cantina energy and 2 refills every day. There was an open window of a week for those spending a massive amount of money to acquire tons of good Mods and that window has been closed with a nerf bat before medium spenders and f2p could enjoy the 100% drop rate of t5 Mods only.
I also think the Mod shipment is insulting customers intelligence when it frequently offers the hardest Mods to obtain ( right slots ones ) with good primary stats at extortionate price. I am glad for CG/EA if they manage to obtain money from obsessed or simple minded people with their commercial practices. I am not convinced this sort of practices and game design either wins in the long run in terms of revenue and reputation.