I started with the 6.5 and think it's a good one when beginners are learning the process of cutting. Some students are not as coordinated in dealing with the length of the larger rulers and space may be limited in the classroom.
I still use my 6.5 and am glad I have it on hand, especially working with the mini blocks, 1/2 square triangles and Quilts For Kids 4 patch units...but I do not cut/use strips as often as others on the board.
OOOH----if you live near a JoAnns fabrics, they have an online coupon for half off that ends today. The other coupon available is for 40% until next Saturday. You can usually do a quick search online for current ones....they're perfect for supplies (and fabric for those of us who never have "enough") :lol: