Rotating cutting mat
 

mine is a 17 x 17 inch square.
i don't know why they didn't make it 18 x 18, but it definitely comes in handy - especially when it's time to square up blocks.

I have the Martelli Roundabout and it is worth the money. No tipping even if cutting on the edge. I take mine to guild retreats and now everyone that goes has one or wants one. I frequently see the green square ones on the guild free table. I have the large one but now there is a smaller size too.

I have a couple of rotating mats and do use them and it nice they rotate. I also sometimes use one of my smaller mats and simply turn them, that works too!

Oh i have one but tend to forget it since it's kept in the cutting table drawer.

I have one and use it to square up hst. At times, usually when I use it, I think about getting a larger one. It's nice when you don't have to move the fabric, just rotate the mat instead.

At a quilt retreat a number of years ago, I saw someone using a round rotating mat by Martelli. It came with the pressing mat too. I know how expensive Martelli is so waited for a sale and bought it. The one I had before never would stay on it's lazy susan section so gave it to the thrift shop for someone else to fight with. Love my Martelli rotating mat and to get it on a sale was a PLUS.

I had a Martelli round one and I hated it. It was hard for me to use, it seemed cumbersome and I had to press down a lot harder than normal. I tried numerous rotary cutters and blades and nothing made it better. I donated it to a quilt guild.

I love mine for squaring up blocks. I find it easier and more accurate since I don't have to pick the blocks up and turn them.

I have the 17" x 17" one from Olfa & I love it. Someone gifted me with a JoAnn coupon many years ago & I used it to buy one when it was on sale. I don't use it a lot but it really comes in handy when I need it.