A active DI is actually a preamp. It dosn't have gain but it is a amp before your board. That brings up questions
Transformer DI raise similar questions
How does this amp sound?
How does the transformer sound?
What is it's noise floor.
How effective is magnetic shielding?
How flat is it?
How flat is the transformer?
What does it do when over-driven?
How is saturation characteristic?
What does it do when it's powersupply changes?
OK no PS in passive DI.
None of the above are show stoppers. Just things to find out.
With a good transformer, you look up the numbers, say "that will work" Now as long as you know that transformer is in your DI and all the switches that change the sound are off you know what will happen when you use it.
Active and passive DI both have their places.
JR
PS: Frank have you ever made an active DI? (I have).