Turface is also called Speedi dri or "OIL DRI" Available at Wal-mart in 50# bags (automotive section) for around $4.15 or close.
Turface is usually a reddish fired-clay product, while Oil and speedi dri are greyish. Great medium. All of these have been Used in Bonsai culture for years to promote root growth delivering oxygen to roots, preventing "dead spots" in the soil, preventing compaction of the soil, and making drainage smooth and even moisture. The increased "breathing" that takes place in the soil does lead to more frequent watering needed, but "overwatering" is really not possible since the soil holds a finite amount of water, it cant hold more. Problems arise only when roots are sitting in "standing" water for longish periods of time.
JC