I hadn't seen (or heard) of these types of pins before. Will have to try them :D

I don't have any, but I have seen them, and read that they are great to use, when working with plaids, as they hold on each side of a design line.
Might have to get some, anything that makes it easier, is A-OK with me.

Yes, they are u shaped and I used them when doing a bargello quilt... had to with all those seams having to match... and used them many many times since... wouldn't be without them... they are expensive here in new zealand... $21 for a packet of 35.

Clips
 

I prefer clips to pins, i get much better seam matching with clips. Clover are expensive. But uou can get small tubs of 50 clips on Amazon for < $10.

I bought some but never really used them. keep forgetting.

I have some, but I found that they were not as easy to use as simply placing a dot of washable school glue where I ordinarily would have pinned.

I also have some and didn't find them to be any better than what I had been using (flat head pins). I thought they bent out of shape easily...at least they did for me.

I think they cost too much money for what you get. I have success with using two regular pins, one on either side on the seam I am trying to match.

I have a package of them but forgot I have them. Therefore I’ve never used them. I’m fussy about my seams so I should get them out.

I thought they were a great idea, and ordered some for the store. The ones I got were so thick, I couldn't get them through my cotton fabric. So, make sure you're getting the thin ones.