I'm a fan of Transient Designer of the first grade... I bought mine on there launch I think now almost ten years ago... and everybody thought I was crazy to spend my money on that strange machine who claimed to 're-liquid' audio... I'm using it since then on almost every project and I'm still loving it.
The proof of it's success is the fact that the price for the TD went up by more than 100% when the item became more known and popular.
In either way we are talking about two different kinds of tools when comparing a TD and a Distressor... If you have to compare (I'm not sure if you can but the Distressor is a compressor, and the TD is rather a kind of gate/expander-like designer of transients
You can't have a studio without considering owning one... that's my humble opinion
Kind regards from Belgium
Pedro