My experience is same as rdchen. I've tried many comparative domestic flight searches and "dummy bookings" on many different routes between ctrip, elong, and travelzen, and results are almost always the same:
1) Travelzen almost 100% of the time DOES NOT SHOW all available flights, so either their software that loads flights is deficiently programmed, or they are selectively showing flights as part of business arrangements.
2) For flights that were directly comparable, I found that ctrip and elong were fairly consistent at giving identical or nearly so all-in pricing, whereas Travelzen was sometimes the same but frequently higher than the other two and sometimes by 20% or more.

This is not meant to steer people away from using Travelzen, and if you can find what you need there at a price that works for you, and you need to use a foreign credit card, then go for it. Just be aware that currently Travelzen has some limitations on what it is showing you on its website. I will continue to run my little experiments every so often to see if this changes, also adding to the comparison mix, alternative sites that many expats here like www.yoee.com and www.9588.com. There is less body-of-evidence compiled about how these last two perform on online bookings done with foreign credit cards from outside China, the sample size is still a bit small.