I don't have straw bales, but deffinately agree ! You can't beat the price and treated correctly, they last a long time.
I have the 18 sided Rheinhart target, though very good but broad heads will make a mess out of it, believe me I found out !
Think about it, if your cutting through something, it's not going to sponge back and reconnect like your skin does because it's not alive. When you shoot a fieldtip, your punching a small hole and more or less just making the target material separate, so it has the ability to rebound back and somewhat fill the hole back in, at least that's my take on it.