Nah. Their UI does need work, but I don't think they make it confusing to make you spend money - after all, what would you spend money on? Money doesn't really remove the need to rank up your mod cards.
Here's what I suggest - when you get to rank 30 in a frame, click auto-install on its mod screen and see what fills in. (You can use auto install all the time, every time you level up, just to have it slot in some useful mods). Play with the frame a bit, and see if you notice any issues, like, if you're too squishy, or don't have enough health.
Then go back to the frame upgrade screen, click mods, and then click on the Vitality mod (if you have one, if not, you'll want to play until you get one). You can use duplicates to rank up mods, but the quickest way is to use fusion cores (they drop in missions). It costs credits to apply duplicates or cores to a card, but when you do, you'll notice the mods are suddenly much more effective.
It does take a while for it all the make sense, but it's not as complex as it looks either. On the upgrade screen, there is a 'tutorial' button that explains some of the basics.