I favor the Apex DT502 over the Sansonic FT300A and Zinwell 970A because its signal bars have a wider range and are more consistent. I think it would help with your evaluation of indoor antennas.
If you look at my posts of calibration of the Apex you will see that it is an inexpensive substitute for a signal level meter and
it gives signal quality readings that are related to BER (bit error rate). I think that signal quality is just as important as signal strength with digital.
With indoor antennas that have a built-in preamp you will be able to see changes in signal strength and signal quality. The only problem that I can think of is that the signal strength bar maxes out in the mid 80 percent range with very strong signals, but the box isn't overloaded. Just insert a fixed attenuator between the antenna and the box to bring the signal strength bar in range again.
But, the Apex DT502 in getting hard to find. All that is left in the local BestBuy stores are DT250s.
The Centronics ZAT502HD isn't a CECB but it has dual signal bars that look just like the Apex signal bars and the tuner is the same:http://www.avsforum.com/avs-vb/showthread.php?t=1136626
You can't add a channel after scan with the Apex, but you can with the Centronics. This is important to people living between two cities and DXers who like to set the tuner on a frequency and wait for a particular signal to come up.
I haven't had any experience with the Sunkey, but it has the same tuner as the Apex DT502 and you are able to add a channel after scan. Trip in VA
has a Sunkey that he uses for DXing.