i am looking into getting a railed forend and am between two companies. the kac free float carbine model or the daniels defense model. do you have to have a mid lengh carbine to begin with to use the daniells defense 9.0? if not it looks like the way to go. what does anyone think on midlengh vs. standard carbine size? how do these manufacturers compare? thanks!

The only way you can think about putting a mid-length forearm on a standard carbine-length gas tube weapon is if the front site has been shaved down.  If you do in fact have fixed front site AR, and it is carbine in length (~7" from reciever to front site) then you will have to get a carbine-length railed forearm.

A way cheaper option is to get a regular free float tube , and have Adco attache rails to it for you .