The bag on the boom is excellent. I wouldn't do it any other way. Quantum will make you a very high quality one for around $100. I got a two-sided one, but it seems entirely unnecessary--I'd go one-sided if I bought another one.

They slide in the track on the boom, so your mains have to be loose footed for this to work. Mains can be easily converted to loose footed if yours isn't.

I think on the Express, putting the spin pole on the boom somehow is necessary. It avoids all concerns about keeping the jib sheet over the pole during jibes, doesn't require the foredeck person going forward to put the guy in the pole, contributes greatly to weather douses, and generally is a very good plan all around. The pole is easily lightweight enough to stuff in the bag.

Other folks don't use a bag but just a couple loops on the boom. Much lower windage and mess, but probably takes a more careful approach to tuck the pole away.