I don't find them tart at all, I find them almost sickly sweet. It's mostly pineapple juice, which is really sweet (to me).
About the pineapple glass: if you order a "lapu lapu", it comes in the pineapple. If you order a "mai tai" it comes in a regular cup and costs about $5 less. (not sure exactly, but several dollars cheaper)
Moral of the story, order a lapu lapu for the first one, and then just get mai tais and pour them into your pineapple to refill. The bartenders encourage this, actually, and are the ones who told me to do so. In fact, they will tell you they don't have lapu lapus at the pool bar, for example, because they don't have the pineapples out there. They can and do make mai tais, however.

Sometimes I get the first lapu lapu with the pineapple from the bar inside, then sit out on the beach and drink it, then get the mai tai refills for my pineapple from the pool bar. And yes, I can drink several of these. I don't find them too strong at all, though YMMV, of course.
