I've got a Fiskars ruler with a built-in cutting wheel that slides the length of the ruler. The whole thing is about 24" long. I've attached a picture below.
Not long after I bought it, the ends came off that hold the cutting wheel assembly on the ruler, and got lost over time. It's pretty useless without those end pieces, because the cutting wheel assembly just falls off the end.
And the measurements on the ruler aren't reversible. If you try to use it with a handheld rotary cutter on the opposite side of the ruler (across from where the black "track" is), you'll get all mixed up.
Even before the end pieces came off, it was very persnickety about completely cutting a strip of fabric. It would leave uncut places along the strip, even with a new cutting wheel. Ugh. I'd have to stand up and lean really hard on it to get it to cut, which was hard on my shoulders and my bad knee. Even DH, who's a lot stronger than me, had trouble getting decent strips. I did like the fact that the blade automatically retracts when you're not using it, but that was about the only good feature.
Other people seem to like it, but for me, it sure wasn't worth the $30 I paid for it (and I've seen it priced much higher). :(
....
On the good side, I love love love my 6-1/2" square and my 12-1/2" square. I wouldn't trade them for (almost) anything! My poor 6-1/2" square has been used so much that the markings have somewhat worn away. :mrgreen: