Yes, DottyD, the 6 1/2 inch square HST ruler is the only size I use even though I bought the 3 pack. I just like having more room for my hand to hold down the ruler as I cut.
Thanks everyone - went to a quilt show in Malvern UK last Saturday and found a lady selling them - so I got the 6.5 " one. She said exactly what you commented on AngelinaMarie about putting your whole hand on the ruler to support it. Pleased with my purchase !! --- and a wonderful show - VERY hot -- for the UK lol !!