I bought a cobra lathe in 93'.. it came with a carbide bit and NO BS,,, i used this lathe until 99 when i came across a deal on a lathe with a diamond bit. It was a shock when the brand new lathe with diamond bit didnt cut all that much, if any better.
I think if your not abusing the bit, it should last for a good ammount of time.
im now using the much more lathe W/ a diamond bit that came with a cobra i bought 2 years ago. Cuts better than any lathe i have ever used.
Keith