The problem with TEs is that it takes a ton of time to figure out which sites actually convert. There are many out there where the credits are gone just as fast as you can pay for them so you'll probably go through a lot of clicks before you see any results.
Another issue is the number of members is no indication as to whether the site converts. You don't know how many of those members are actually still active.
I won't say that they are a total waste but if you need high converting traffic and you have limited time, it might be a better idea to try other methods for getting traffic first.