Should i use mercenaries or not as I don't know if they are viable or not? Also if I should use them should I use them on all levels or just the beginning ones?

mercenaries are super useful. I do try to delay so I can spend money upgrading my engine first. I don't know if it's optimal, but my general rule is that I will buy mercs as soon as the my money income / army income is about 5-10x the cost of the mercenaries.

ex. money income is 120k, army income is 10k, I will buy any mercs that cost $1.20 for sure and maybe up to $2.40.

ah ok thx i was just wondering if i was wasting my time spending money on mercenaries.

Mercs are super useful. Not using mercs would vastly slow down your speed to finishing a level.

Mercs are essential power that must be used.