In general when I use a transient shaper, I insert a compressor/limiter after it, so I don’t increase the peaks of the signal. The illusion with transient shapers is always “overdoing” it and making things unbalanced again, so the limiter keeps the sound under control.
You can actually do a good comparison: 1. Increase the transient or 2. decrease the sustain and check what sounds better. Sometimes an increase in the sustain can be more natural, the signal is getting “compressed”. So it’s similar to “compressing” a signal.
Setting-wise I wouldn’t go crazy on the BUS. 1dB can make a huge difference. On a single track, 5dBs can work, depends on the mix of course. More than 5-6dB it’s getting unnatural. The human ear doesn’t require a lot of volume-gain, to find that something is more “snappy”. 1-2 dB work in most cases.