I'm all about sentimental value in my wiser years. It was a bit of a debate between the necklace and the flag that we bought when we ourselves were in Italy. The necklace has more sentimental value but the flag does have a lot as well.
It's funny, my sister is engaged to a real scum bucket and he thought I was stupid for wearing an engagement ring myself. Now that my sister is engaged to the prick I told her he should wear one and he made it very explicit he will not be. Class act, that chap! I rather liked the concept of men wearing an engagement ring. I got a lot of talk at work about it and all the women I worked with loved the idea. I want others to know my wife is taken why not let them know I am? Modern times!
Sounds like you've got some fun times ahead with your brother in-law, although if he's such a tool-bag chances are she gets rid of him before it goes too far.
I never wore an engagement ring, but I know a few guys who did. Nothing wrong with it.