I am just having the 12 week and 19 week. As the others aren't really necessary unless there are concerns I can't see the point. I wonder what it would be like for the baby being pushed and prodded with that thing just for our benefit (ie just to have a look). As some prominent doctors such as Sarah J Buckley have noted, the safety of ultrasounds still have not been verified Ultrasound Scans- cause for concern.
I guess like any test you may need to have, it's good to be informed about the pro's and con's.