using index cards as minis trays/units

kind of curious about the feasability of this and interested in feedback

basically I don't have the patience or energy or motivation to paint minis and I don't really have money to buy them and I did some research on alternatives

I discovered there is a series of games called "Battlegrounds" that uses cards to represent an entire unit on the table

and that got me thinking that Grimdark Future has rules for things like unit trays or small minis put together in groups on bases

the rules for GF basically says actual dimensions of things don't matter too much as long as you're consistent about it

so this is my idea

everything is just a 3x5 card

if it's a squad of guys it's an index card

if it's a group of bikes it's an index card

if it's a tank it's an index card

if it's a big scary monster it is an index card

how well would this work and could anyone forsee issues with it?