First I would never buy mods in mod shipments.
Some could also say wasting resources on a 5 dot mod is useless as 6 and 7 dots will be in the game soon.
For the leveling costs and randomness and stat gains Mk3 are not bad
Same energy cost as MK1/Ml2 and way cheaper than MK5 to level up.
MK3 costs 152K credits
MK5 costs 474K credits
Not counting secondary stats
5 Mk5 health mods with 4 x 5.88% offense = 23.52 % offense add
4 Mk3 Offense mods with 2 other mod sets = (4 x 3.88%) + 10% = 25.52 % offense added
So which character hits harder
Added offense difference is 2% per mod primary
If you only shoot for MK3 mods you don't have to have fully maxed teams to beat T1 of the challenges.
So now I can do something like add 15% crit chance to Rey. Sure she will lose that 8% offense but will be crit hitting more.
Just my opinion on this.