I've been looking forever for a product that would solve my 'crack' problem.  Most of my pants are cut low, so the majority of my shirts are too short.  Also, when I sit down, the pants tend to show off more than I want people to see.  I've seen similar products for non-pregnant people but they were too small to do the job.  They rolled down a lot and I didn't get the coverage that I wanted.  I saw these on Amazon, and though they were a little pricey, I decided to try them out.  Major difference!  They're very thick and well made, and much longer than similar products I've seen.  I use them under my shirts all the time to cover up the 'gap' and they work great.  Unlike other products they stay put.  No more constant adjusting when I sit down or move around.

About sizing:  I would say it's pretty much true to size.  I'm normally a size 5-7 and the size 2 fits best, though I can fit into the 1 also.  For anyone who's pregnant, though, I would get some larger ones for later on.  I couldn't imagine squeezing into a size 2 when I was 8 months along with my kids.  They are spandex, though I don't think they stretch quite THAT much.

Though some of the patterns are fugly, there's enough colors/designs to make everyone happy and match a good deal of your wardrobe.  I have three different colors so far and plan to buy more.  My only regret is that didn't find these sooner.