I'll throw in my $.02 here,
I have used, installed and critically listened to most of the CDT product line. IN CARS!
The ES 02 is a MID Tweeter, it can be used in a 2 way system but it does have some roll off in the very top end. It could be easily corrected with some eq'ing. I would personally use it, but if you like a really crisp sound consider combining it with a super tweeter or in a 3 way system.
The ES 01 is considered to be there "audiophile" tweeter. It has a very flat response. Some people like it, some don't. It really depends on your listening tastes.
DRT-26 is the tweeter that, in my experience most people perfer in listening tests. It has a small frequency response bump in its output that many find appealing, including myself.
Hope that helps.
-Jay