well considering that you can get 243 bullets all the way up to 105 grains it is a really good compromise between 223 and 300 blackout. blackout not only trims the casings back but also dumps a heavier bullet with a not so great ballistic coefficient and then tries to send it at very low velocity.
keeping the full length casing and reducing the amount of sizing needed prolongs the life of the casings and allows for stronger loads and the 6mm bullet still packs double the weight of the average 223 without sacrificing too much velocity and shoots fairly flat within 500 yards.
for target shooting yes the 223 is much more suitable but for hunting I would love to have a 6x45 for deer and just about anything else short of elk. however even right now while ammo is high and reloading supplies are still pretty available and cheap-ish, it's still cheaper to pick up a 1024 round spam can of 5.45 than it is to get 1000 223 casings, wildcat dies, 1000 243 bullets and 8 pounds of your powder of choice...
it'd be a better choice for hunting but if all a guy wants is something different in his gun safe and something that won't break the bank then a 5.45 AR would do just fine.
all guns lost in a tragic smelting accident.
I never said half the crap people said I did-Albert Einstein
You can't believe everything you read on the internet-Benjamin Franklin
Bean counters told me I couldn't fire a man for being in a wheelchair, did it anyway. Ramps are expensive.-Cave Johnson.