Promise ring advice


So my boyfriend and I are planning to get engaged in about 2.5-3 years from now after we finish our undergrad. We both already know we are gonna get married but have only been dating for around 8 months. It's one of those "when you know you know type situations." My family already knows it's a plan, but his family not even close to being updated on our intents with each other (very traditional) and not as quick to accept the idea. He is the baby of the family with sisters 5 and 8 years older who are both single. I plan to transfer schools next year and I just really like the idea of having an outward symbol of our love for others to see and understand, but not have it be the big change of an engagement ring. He is hesitant to think about an engagement until his sisters have something happen but who knows when that will be. Is a promise ring a good middle step since we can't be engaged for a while but know that's the direction we want to go????