They certainly slow the game down a little, directing attacks away from opponents, much in the same way planeswalkers mightalthough one could argue that the benefits the battle offers will help wrap the game more quickly down the road
Is your purchase driven by nostalgia
Based on the latest market prices tracked on TCG Stacked, Imaginary Friends is worth about $0.91 USD
Convoking this with humans is likely to keep some key threats in play, whereas tapping down a pegasus or kithkin is more likely to sweep the opponents boards
Being a Fire type is pretty good, being able to hit Dialga G LV
Or maybe you have another, no less sneaky plan which I havent figured out yet :) The total power of tapped creatures is calculated before those are actually tapped, so Sword of the Paruns isnt of much use here