With a steel base ring like you'd get with Mature Metal, from experience the shape can matter. For me, a "correctly sized" circular ring gets...
I think if you have a somewhat reluctant parter, you maybe have to carefully think through how to make it feel like a win-win thing for him...
To think that I got my brand and there wasn't even any chastity involved... I guess I'm a pushover ;) Anyhow, congratulations, hope it brings you...