Iirc correctly, you pick it up and it explicitly mentions it has "Sub-Tuner" on it and you then have the option to either leave it where you found it or put it on, so it's similar to the Urbolg scene in that its pretty sign-posted.
If you put it on Belle you go subby pet mode and Belle comes and collects you. She explains what the collar does and then it goes into one of her scenes that goes something like Spanking > Walkies > Blow her > Get fucked/Fuck Saec ( her other pet) and then you're free to go. After that you can go back and talk to her without doing any of her scenes if you don't want to. Unlike Urbolg collar/Badger/Jasvalla there's no bad-end associated with Belle.
Personally I'm a big fan of the sub-tuner stuff and I'd love to see similar content elsewhere as well as more Vava Groom but I don't either would happen anytime soon </3
The reason it triggers me is how the quest is presented. Yes, it is very dumb to just snap an electronic collar on your neck. But everything that follows removes any choice in how to react. And I don't mean the literally being hypnotized part-I mean how Steele deals with it after the fact. There are no options to express your discontent. If you proceed further, your crewmates and friends can even react positively to your situation. So from my perspective, the PC is being slowly brainwashed to not notice any of the glaring red flags in this situation and either others just think you're doing petplay or legit think it's fine. Oh, and then she puts a barcode on your ass, while you are not capable of refusing. This could be straight out of my nightmares at this point.
If you like Belle, great. I don't want her literally out of the game. I disagree that picking up the collar braces you for what to expect, certainly not well enough. Because the shock of it was part of what triggered me. And I do mean trigger, as is taking deep breaths trying not to have a panic attack triggered.
I also love Vava Groom. Kinda the polar opposite from Belle actually. Once reads as slavery-by-another-name and the other is presenting the same relationship as mutual, supportive, loving and 100% consensual where everybody knows what everybody's lines are. It's why I replied to your post about Anyx, I think she is one of the best dommes Steele can have; perfect blend of aggressive and caring. Sera's good in the opposite way, a complete bitch but actually respectful of your boundaries; everything she does to you is something you signed up for.
Also how about some Brat Sub Steele where acting the brat isn't considered a 'fail' or misbehaving, but the goal? Maybe service-top Siegwulfe? These are just thoughts.