I do use the signal follower for this. Mostly because it is the only device with actual lookahead. But I learnt it is often better to utilise artificial inputs instead of letting it analyse the actual audio, especially for bass.
One trick to make it behave in controlled ways, is to use dc samples in the instrument you want to duck things to. You know, a 1-sample loop with maximum value set via sample drawing, turning off the key/pitch in the keyzones, velocity to your liking. Put the keyzone spanning each key of the instrument that you want the sidechain to react to. Then you define the shape of the ducking via a volume envelope for this sample. The sample should be routed to an extra instrument fx chain, and from there to some sort of dummy track. In the dummy track you use the signal follower to process the envelope, and a gainer right after which will mute the dc sample, you don't want it mess up your audio.
It is a bit of a hassle to set up right the settings for the signal follower, because sensitivity will make peaks be different with attack/release changed. What I do is vaguely adjust the sensitivity so I get proper ranges, tune the attack/release to my taste and then adjust sensitivity up from a low position, with a +1 dc sample feeding into the device, so it will just touch the top of the bar to the right of the device.
Maybe you will wish to compress/limit the signal if you use polyphonic action. Also if you wish to mix the sidechain signals from multiple instruments - all no problem. Just make sure you always somehow mute the dc signals before they hit your master or sound card outputs, there's no value in listening to them, and I think they might even be dangerous for some speakers.
I would then of course use the signal follower to control a hydra, and from there some kind of effects making things react, i.e. a gainer or compression or gate threshold on the 100% wet reverb send, or the track that some instruments would send their ambience sounds if they are encapsulated.
You can also modulate the "analytical" dc signals with a gainer or other modulation means, for example if you wish a sidechain to react to a filter modulation, or similar tasks. And you can of course set up multiple different sidechains per note/instrument.